Why did the Allies Invade French North Africa?

Your question gives two separate issues for the justifications of the choice of Operation Torch by the Allies:

• First, why did the Allies attack in North Africa rather than in Europe directly (e.g. Operation Sledgehammer). This was an "intra-Allies" issue, because Americans wanted to attack directly in Europe whereas British preferred "peripheric operations" and wanted to secure the Mediterranean Sea
• Second, why did they attack in North Africa in a French-hold zone, rather than directly on Axis forces in Libya and Tunisia? Once you answer the first question, you enter this new issue. This is a political issue (should Vichy remain in North Africa?) and a military issue (Were Allies able to land close to Axis forces)?

You should try to get information on those two points to make your question more specific.

EDIT: Details on the different factors

Considering the comments and existing answers, I will detail this answer not on how American officers were forced into "Torch" operation, but on:

• Why did British want a peripheric operation?
• Why did Americans were in favour of an head-on operation?
• Why the location of "Torch" ?

First, the British "peripheric strategy": This is something coming from as old as the Napoleonic Wars. During WW1, the British fought head-on and had a bitter time on the land and in the air. However, on the sea, they applied with success a strategy of containment of German actions in the Atlantic Ocean and Austrian ones in the Mediterranean Sea. They also managed to act successfully against the Ottoman Empire, in the Sinai for example by repelling Ottoman attacks and triggering rebellions with the famous "Arab Lawrence". However, again, head-on attacks against important Ottoman positions were fails (not really defeats, though) at Gallipoli and in Mesopotamia.

At the beginning of WW2, one should remember that British Army was beaten nearly everywhere. It is only far from the metropolitan territories of their ennemies (Germany, Italy), with capacities to hamper ennemy logistic lines, that British and the Commonwealth forces succeded in defeating their ennemies: Italians in East Africa for example, Vichy French in Syria and Lebanon, Iraqis rebels.

When USSR went into the fight, they had the opportunity to apply a peripheric strategy "Napoleonic-style", and for that they sent supplies to USSR. They continued to fightthe Kriegsmarine, to defend Egypt, but USSR wanted direct attacks against Germany.

Thus, Britain started bombings on Germany. By night on cities: A very peripheric way to strike German armies, but a way that could reveal efficient. They also tried commando actions: Successes in Norway, far from Germany. Fail at Dieppe, in front of an heavy German defence (though a succes of attrition in the air).

So when Americans come in with their new army, not experienced, and say: let's attack on European coast, the British have good reasons to tell them: "You're foolish, we can't attack either as a raid or as a liberation operation. But come with your planes and ships."

Second: Well, that's an easy point:

• If you want to win against Germany and Japan, you don't take your time. You have human and hardware potential, you should use them as soon as possible
• If USSR asks you to do that, or they might conclude separate peace, you're truly in a hurry So Americans wanted at first a direct attack against Germany.

But the point is that they were wrong: their army would have been slaughtered in such an action, either a raid or a true invasion of Europe.

Third: Considering point 1 and 2, the British suggested to help dommed the Axis in Africa, a peripheric success that would lead into an attack against Europe later. Americans accepted because the understood it was better to start cool.

Why did they land in the French zone of Africa? They had no choice and Free French pushed them into such an action.

• Landing directly in Tunisia is dangerous because of Italian navy, Axis aviation and AfrikaKorps and Messe army in Tunisia
• Landing in Maghreb gives enough time to constitute a solid army before fighting Axis
• Free French wanted to impose as the new France: Americans and British still had doubts on a military (De Gaulle) wanting to be the new leader. For Torch, Allies took contact with French and soon realized that it would be a definitive test: Either Vichy in Africa rallies to them or fights them. It apperared in the end to fight briefly, "for honour" somehow. In the end Free France invested successfully the zone and created new army from the population in North Africa, but that's another story.

So to conclude, landing in Maghreb for Torch resulted in:

• Assess a political situation
• Achieve a peripheric success against a former dangerous force
• Prepare for actions against Europe (especially Italy)
• Make American forces face a true fight and gain in efficiency

Roosevelt's Political Imperative
Roosevelt was of the view that US public opinion required immediate successful military activity by US forces before the end of 1942. As others have stated, an election was to be held late in that year, which must have been a factor, but in general ensuring continued public support for the war effort was always an important consideration for the US leadership. The joint decision by the United States and Britain to pursue a 'Germany First' strategy precluded an offensive in the Pacific in Roosevelt's eyes, as he believed this would upset the agreed Allied strategy and run the risk of damaging or wrecking the coalition. Similarly his "promise" to Stalin that a Second Front in Europe would be opened up in 1942 to take pressure off the Soviet defense was also something Roosevelt did not wish to back away from.

Strategic Considerations
With the preferred option of the US Joint Chiefs of Staff of a Pacific offensive off the table, US military leaders were faced with choosing between the only two realistic options available to them in Europe:

• The 1942 cross-Channel invasion of France code-named SLEDGEHAMMER.
• The 1942 invasion of French North Africa code-named GYMNAST.

The SLEDGEHAMMER cross-Channel invasion of France was overwhelmingly supported by US military commanders, who felt that GYMNAST was a strategically pointless operation which was motivated by British imperial interests and which would result in a dispersal of effort and most likely cause the 1943 invasion of France, code-named ROUNDUP, to be delayed until 1944, thus providing no immediate relief for the Soviets in 1942 and delaying the actual proposed 1943 Second Front for yet another year.

Roosevelt, on the other hand, supported the British in their belief that the Mediterranean was a vital part of the European theater, and that operations there could achieve meaningful gains against both Germany and Italy. British planners had determined that a 1942 SLEDGEHAMMER invasion of France was possible, but only on a limited scale, and as such would not provide meaningful relief for the Soviet Union, and would have little value in keeping them in the war. As the survival of the Soviet Union was believed to be still in the balance in mid-1942, it was felt to be too great a risk to land forces in France only to have them thrown back into the sea should the Soviets collapse. This would be an unacceptable political disaster for both the British and Americans.

The Decision
The GYMNAST invasion of French North Africa offered the possibility of an easy military victory in 1942, which would secure the North African coast, and create a base from which British and American forces could continue to operate into Europe and the Middle East in the event of a Soviet collapse. The threat to the Atlantic would be significantly reduced, and Allied logistics into Europe and the Middle East placed on a more secure footing. The map below shows clearly the improved situation in the Atlantic resulting from the conquest of North Africa. A key moment of decision seems to have been the agreement between Roosevelt, Harry Hopkins, and Churchill, in mid-1942, that GYMNAST would not cause a delay to the 1943 ROUNDUP invasion. With this understanding, Roosevelt gave the order for the invasion of French North Africa, now code-named TORCH, to proceed before the year's end.

The above is sourced from the excellent:

Allies and Adversaries: The Joint Chiefs of Staff, The Grand Alliance, and U.S. Strategy in World War II, by Mark A. Stoler (2000)

Map from Hyperwar

Contrary to the general statements that the invasion of Africa was of no benefit to Russia - Stalin personally expressed approval of the African and Mediterranean operations. Without the African invasion Italy would have not needed to retain the number of divisions it did - and Field Marshall Kesselring's very capable services could have been used to advantage elsewhere. ['Smiling Albert' served in a major role, usually with reasonable distinction, in more theatres than almost any other major German leader].

Torch was the precursor to Sicily and Italy.
The German capitulation in Africa lost the Germans a large number of competent and battle hardened troops. (As well as losses during battle, about 150,000 German and 100,000 Italian troops surrendered after operation torch and over 100,000 French forces who had not already been "captured" subsequently joined the Allied war effort).

The invasion of the European mainland in 1942 would have been an utter debacle for the Allies. At that stage the US conception of what was involved was severely lacking. Africa provided a very good grounding for the later US competence in Europe.
To quote Wikipedia

• In the west, the forces of the First Army came under attack at the end of January, being forced back from the Faïd Pass and then suffering a reversal at Sidi Bou Zid on 14–15 February. Axis forces pushed on to Sbeitla and then to the Kasserine Pass on 19 February, where the U.S. II Corps retreated in disarray until heavy Allied reinforcements halted the Axis advance on 22 February. Fredendall was replaced by George Patton.

After that .... :-)

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The comments on "what Stalin thought" brought to mind this 'analysis' written immediately after the 1942 Moscow conference.

While jocularly put (in the extreme :-) ) this poem of Wavell's summarises the conclusion of what was concluded at the 1942 Stalin-Churchill conference in Moscow. Written by Wavell in a bomber (used as a transport aircraft) on the return flight. From here

I just wanted to add an angle which I didn't see included in sempaiscuba's answer which I voted for and accepted. Sempaiscuba went into the US domestic political motives which contributed to FDR's desire for American forces to see action in the European theater in 1942. But why North Africa on the Nazi's periphery, why not a cross channel invasion as FDR's military advisers were unanimously recommending. As FDR and Churchill had promised Stalin, A second front in Europe in 1942.

Second Front
At Teheran, Joseph Stalin reminded Churchill and Roosevelt of a previous promise of landing troops in Western Europe in 1942.

Short Answer:
It was Churchill with unanimous support from the British general staff which refused to support a cross channel invasion in 1942 favored by the US Military. Churchill had been lord of the Admiralty during the disastrous Gallipoli landing which gave him a hyper appreciation for the risks of large scale amphibious landings. One of the primary risks which Churchill and the British General staff were concerned about was the untested American Army. Churchill lobbied for smaller peripheral operations as a way to give the US army experience before he would commit British forces to support a cross channel invasion.

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Detailed Answer
All of FDR's joint chiefs of staff, his secretary of defense and his Army and Navy Top Commanders Marshal and King disagreed with Churchill on operation Torch.

General Marshal went so far as to suggest to Roosevelt that the U.S. abandon the Germany-first strategy and take the offensive in the Pacific. Roosevelt "disapproved" the proposal saying it would do nothing to help Russia.

Admiral King and Admiral Leahy the Chief of US Navy Operations and the Chief of Staff to the Commander and Chief respectively, both strongly favored the Europe First strategy "but so long as "it was doubtful when—if ever—the British would consent to a cross-Channel operation they disliked sending to the United Kingdom american men and materiel which were desperately needed in the war with Japan."

George C. Marshall: Organizer of Victory 1943–1945. p. 305. by Forrest C. Pogue (1973)
At the Casablanca Conference, King was accused by Field Marshal Sir Alan Brooke of favoring the Pacific war, and the argument became heated. The combative General Joseph Stilwell wrote: "Brooke got nasty, and King got good and sore. King almost climbed over the table at Brooke. God, he was mad. I wished he had socked him."

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Rethinking Roosevelt as Commander and Chief
In “The Mantle of Command,” Hamilton details how Roosevelt overruled the Joint Chiefs of Staff, Secretary of War Henry Stimson and U.S. Army Chief of Staff George Marshall when they strongly advocated an invasion across the English Channel in 1942 to open up a Second Front.

The US Military was frustrated that all the logistics and troops being prioritized to Europe were being stock piled and were not being used.

The primary opponents to opening up a front in Europe in 1942 was Churchill and his military advisers who convinced FDR to postpone a cross channel landing. Churchill argued for operation Torch a landing in French North West Africa where the Americans could expect little to no opposition. The French soldiers were former allies, and the French generals in charge of those soldiers were eventually negotiated with to cease their opposition after relatively few casualties for an invasion of similar magnitude.. ( about 500 American's died. )

OPERATION TORCH AT 75: FDR AND THE DOMESTIC POLITICS OF THE NORTH AFRICAN INVASION Even as late as June 1942, the decision to land in North Africa was anything but assured. It was one of several potential operations being debated by the Combined Chiefs of Staff, and Roosevelt did not even approve the landings until the end of July. U.S. military planners were almost universally against the North Africa landings, feeling the United States was being drawn into a peripheral war to protect British colonial interests. Instead, they favored the logistically intensive cross-channel invasion plan known as Roundup because it took a direct approach and would be able to draw additional German units away from the Eastern Front. However, Churchill and the British chiefs of staff were unanimous in their refusal to support a cross-channel invasion until American troops had been battle-tested. Despite the apparent impasse, Roosevelt remained adamant that an offensive action occur in 1942, going so far as to promise Soviet leader Joseph Stalin a second front before the new year.

The first time the United States army did come into direct contact with the Nazi's would be Feb of 1943, 4 months after Torch, Kasserine Pass: America's Most Humiliating Defeat of World War II where the US would be routed, inspiring Eisenhower to begin to make changes in leadership, organizational components, and tactics.

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As for the FDR's Political Problem

George C. Marshall and the “Europe-First” Strategy, 1939–1951:
Stimson warned Churchill in the summer of 1943 that “only by an intellectual effort” had the American people “been convinced that Germany was their most dangerous enemy and should be disposed of before Japan”; the enemy they “really hated, if they hated anyone,” was the one that had “dealt them a foul blow” at Pearl Harbor.17 Throughout the war, Marshall as well as Roosevelt remained aware of this, and with it the fact that public patience was not limitless: victory over Germany had to come quickly or public pressure, supported by the Navy as well as MacArthur, might force a dramatic shift in U.S. global strategy

FDR did have a political motivation to see American troops involved in 1942, but it wasn't solely the elections of 1942. Every other year is an election year in the United States and FDR had a 60% majority in Congress and a 71% majority in the senate. Even with Operation Torch occurring Nov 8th and election day occurring Nov 3, 1942 the democrats retained a 20 seat majority in the senate, and a narrow majority in congress.

After pearl Harbor the First War Powers act of 1941(Dec 1941) and Second War Powers act(March of 1942) gave the President sweeping authority to conduct the war as he deemed fit. The President's new war powers came at Congress's expense and were legislatively mandated to stay in effect until six months after the war had concluded. Congress's major legislation in 1943-1944 are almost laughable considering the US was a country at war spending hundreds of billions of dollars and dramatically changing all aspect of the citizens lives. Congresses role in this period was largely restricted to planning for soldiers leaving the service.

• 12/17/1943 Chinese Exclusion Repeal act, Congress agreed to allow immigration from China.
• 2/3/1944 The Mustering out Payment Act,
• 6/6/1944 The Serviceman readjustment Act
• 6/27/1944 The Veterans Preference Act
• 7/1/1944 Public Health Service Act
• 12/22/1944 The Flood Containment Act

FDR's political problem was that millions of Americans had volunteered for military service, the US had retooled the entire economy to put it on a war footing, Americans were facing rationing of food, consumer goods, and transportation. A significant portion of that material and most of the men coming out of training was going to Britain. Politically that looked terrible if they weren't to be used. FDR's political problem was thus one of public relations rather than domestic politics alone.

FDR's need to show military progress in 1942, was somewhat satisfied by action in the Pacific War.

• Doolittle's raid on Tokyo April 1942,
• Japan's defeat at Coral Sea May of 1942,
• most especially the Battle of Midway in June 1942, called turning point in the Pacific War,

These events especially Midway, freed up Roosevelt's hand to agree to the UK's insistence on Operation Torch in July of 1942.

There is no doubt Stalin preferred the 1942 cross channel European front he had been promised. Stalin wrote Churchill a letter August 13, 1942 after being briefed on Operation Torch attesting to his preference.

In Retrospect the United States did reevaluate it's Europe first strategy. Today we know that in !942, until dec 1943 the United States sent more men and equipment to the Pacific. It was not until early 1944 when preparation for the Normandy landings, that American forces in Europe surpassed those in the Pacific. And even in 1944 the policy of fighting Germany first was absent as the US pursued major offensives in the Pacific like the Philippines which committed 1 million US forces just 4 months after D-Day. see:

• American First Analysis

It is true that the US was asked to maintain 3 divisions in Australia in early 1942 at the request of Winston Churchill. However the United States had 95 Divisions in WWII almost all active by the end of 1942. The Three divisions protecting Australia does not explain why the United States had more troops deployed to the Pacific until Dec 1943. And European troops did not exceed Pacific troops until early 1944. At best this troop and logistical deployments demonstrate that the US turned away from Europe first in 1942 and pursued a relatively balanced two front strategy. Just as the US General Staff and Presidential Advisors had told the British they would in leading up to Operation Torch.

US Military Manpower by year 1789-1997