Was the Zimmerman Telegram a ruse on the US or a way of Germany to incite Mexico to declare war on the US?

Most arguments to this being real are often flawed. There was very little German involvement with Mexico. Also the Germans denied the writing of the telegraph. Also, the British cut the German telegraph line with the America's. Also there was also evidence to point to France writing the telegraph in German. The final argument I have is that the US was not an allied power and wasn't going to be until a direct threat was made,thus the Germans had none to fear.

Question: Was the Zimmerman Telegram a ruse on the US or a way of Germany to incite Mexico to declare war on the US?

The Zimmerman Telegram wasn't a ruse but nor was it the casus belli for US involvement in WWI.

The way we can be certain the Zimmerman letter was genuine even before Zimmerman gave a press conference in Germany to defend his letter, admitted it was from him, is in the nature of the transmission of German communications with Mexico. The reason he admitted ownership was because it was pointless to deny ownership. Ownership was readily verifiable.

You see Britain had cut all of Germany's transatlantic cables. Their only way to communicate with their oversea embassies in the America's was to hand their communications ( encrypted ) to the Neutral Americans in Berlin. The encrypted message was then Currier-ed / sent by the American Embassy to Great Britain were they would be telegraphed using British trans Atlantic cables, encrypted along to New York and eventually to the German embassy in question, in this case Mexico City. Great Britain allowed this "service" by neutral America; because Britain had broken Germany's code and could read the encrypted communications. It was Great Britain who made the United States aware of the contents of the message and it was irrefutable because of coarse the United States could independently verify the decrypted message the British showed them was the same message they had received from the German ministry for transmission across the Atlantic, because Britain also shared the decryption details.

I say it wasn't the casus beli for US entry into WWI because Germany's renewal of unrestricted submarine warfare was probable more deterministic as was private American financial interests with France and Great Britain as organized by JP Morgan. By the time the Zimmerman letter came out the United States was already fairly well down the path to entry into the war on behalf of the allies.

P.S...

While Mexico never fought against the US, so was this even a possibility?

Actually the Zimmerman letter occurred January 1917. Poncho Villa raids into the United States on behalf of the Mexican government one of which resulted in the Battle of Columbus, New Mexico with the United States Army occurred March 9, 1916. The United States invasion and seven month occupation of some of Mexico's territory was also fresh.. April 9, 1914 Battle of Veracruz. U.S. President Woodrow Wilson considered another military invasion of Veracruz and Tampico just after the Zimmerman Letter in 1917 and 1918, relations were so poor. So US Mexican relations were definitely a sensitive spot just prior to WWI and had erupted in military action by both sides just before the letter was revealed, which of coarse is why Zimmerman proposed the "agreement"/understanding with Mexico should the US enter the war.

Firstly, the Zimmerman telegram was real and sent, he admitted so himself at a press conference.

Secondly, it was a feint to turn Americas attention away from the war in Europe and towards a possible one against Mexico. Germany feared Americas involvement in the war and wanted to ensure they were more concerned with one closer to home. There was no serious plans from Germany at all to support a war between Mexico and America.

Thirdly, The American government thought the telegram was fake when told about it by the British government and thought it was a ruse being used by the British to involve America in a war most of their population were against.

Germany sent, or tried to send the "Zimmerman telegram" to a Mexican government that basically didn't exist. Americans initially thought it was a "ruse" by the Allies until Germany's Arthur Zimmerman admitted to sending the telegram, as pointed out by one of the posters.

The reason was that Mexico was in throes of a "free for all" civil war at the time, which is to say that it was in a state of anarchy.

The reason the Germans thought otherwise was because the most unruly of the four major factions, the one under Pancho Villa, "invaded" the United States, crossing the Rio Grande to escape from the others. The Germans reasoned that the Mexicans were trying to recapture Texas and New Mexico, so they offered "Mexico" Arizona and California as well, all of which Mexico had lost to the United States in the 1830s and 1840s.

America's General John J. "Blackjack" Pershing soon launched a counterattack that pushed Pancho Villa back into Mexico. Then he led American forces that ultimately won the First World War from Germany.