Why did Canada, Australia and New Zealand separate from the UK?

We should note that many of the people in these places are NOT of British ancestry. The French Canadians of Quebec come to mind - they certainly were not eager to be British subjects, but were more willing to support an independent Canada. Australia also has a large population of Irish ancestry who, again, probably were not thrilled to be ruled by Britain.

Independence from the UK was less important to the creation of Canada and Australia than federation of independent colonies were.

Immediately prior to federation in 1901, Australia was effectively six independent nations. All part of the British Empire, true, but largely run from their colonial capital cities. Federating the colonies into the nation of Australia was much more about getting the colonies to work together than it was separating from the UK. Before federation, there were massive import duties on goods crossing colony boundaries, and all sorts of other impediments to interaction. The forming of Australia was not entirely unlike the forming of the EU.

After federation, the UK still controlled Australian foreign policy for some decades, there was no such thing as an Australian citizen until 1936, and the UK's highest court could still be appealed to from Australia's highest court until 1986. There's been a gradual migration of powers moving from the UK to Australia since the UK first settled the place.

I am less familiar with Canadian history, but I understand things were similar there. Newfoundland was a special case where the locals preferred ties to the UK to Canada until 1949. And even then, the referendum to join Canada only just passed.

In the case of US independence, that wasn't a case of everyone in all the British American colonies suddenly deciding to separate because they no longer felt British. It started with a tiny number of people who didn't like what their government was doing. They decided to fight their local government authorities, picking up more support over time. After taking over the middle 13 British colonies, they decided to stop. They spend up the transition of power about 100 years, and in doing so stopped the resulting federation from including what's now Canada and half the Caribbean.

For Canada, many reasons brought it to independence.

First of all, colonies were taken and land was captured so metropolis could exploit natural resources there. Canada was thought to have gold (and a way to go straight to China, the Northwest passage).

Finally, none of these were proven, and the most wanted resources were

1-fish

2-beaver fur

3- wood (especially during Napoleon's blocus)

At the end of 19th century, these resources weren't as attractive as they used to be.

Also it was quite costly to maintain troops there to prevent a US attack (like the one that occurred in 1813). Great Britain clearly had other more valuable interests elsewhere around the globe, so they gave Canada permission to create a confederation in 1867. The country wasn't completely independent though, as it was still part of Commonwealth. We can see effect of that during WWI when UK declared war for Canada. But it was only after the war, where Canada had proven its value, and the UK lost prestige and wasn't the 1st nation of the World that Canada was really given autonomy with Westminster Status in 1931.

Even with the Constitution being brought back to Canada in 1982, Canada is still part of Commonwealth and the real leader of the country is still the Queen. Every bill voted has to be signed by her representative, the governor. You can note this role is only symbolic.

Actually the perception of these places being independent is much greater then the actual degree of separation. In Canada for instance they had to ask the queen for permission to dissolve the parliament.

Fun fact: Canadians pay more per capita in taxes to the queen then the British do. Approximately 1.54 per capita vs the 1.32 that the English pay.

Added Source as requested for above comment: Maclean's

There are a few reasons that the Australasian colonies decided to federate – and the emphasis will differ depending on which (historical) person you ask. If I may use a modern comparison, there a few reasons that Australia did not become a republic when the referendum was put to the people in 1999: there were various groups and people advocating the “Yes” or “No” positions, and each group/person did so for different reasons. Saying that it was simply that Australians didn’t want to become a republic is simplistic.

Similarly, we can not point to any single reason and say “That is why the colonies decided to federate!” There were many reasons and motives proposed by many people and organisations over a few decades, and they all contributed to the final outcome.

As early as 1857, a Select Committee in the recently formed colony of Victoria wrote:

Your Committe are unanimous in believing that the interest and honor of these growing States would be promoted by the establishment of a system of mutual action and co-operation among them. Their interest suffers, and must continue to suffer, while competing tariffs, naturalization laws, and land systems, rival schemes of immigration, and of ocean postage [...] exist; and the honor and importance which constitute so essential an element of national prosperity, and the absence of which invites aggression from foreign enemies, cannot in this generation belong to any single Colony of the Southern Group; but may, we are persuaded would, be speedily attained by an Australian Federation representing the entire.

[...] By becoming confederates so early in their career, the Australian Colonies would, we believe, immensely economize their strength and resources. [...] They would not only save time and money, but attain increased vigor and accuracy, by treating the larger questions of public policy at one time and place.

[Report from the Select Committee upon the Federal Union of the Australian Colonies, 1856-7]

Note the various reasons listed for federating: tariffs, citizenships, immigration, postage, defense, efficiency.

In 1870, Charles Gavan Duffy spoke in the Victorian Parliament about this previous Select Committee report. His main point was that there had been no action on this report for too long. In pushing for action, he said:

It may be said, no doubt, that England is mistress of the seas, and will be able to protect her commerce and ours. But France and America have been making enormous expenditure and immense exertions for years past to be in a position to compete for this supremacy. Even if it be admitted that England would be able to protect the great highway to Europe by the Cape, will she be able to guard the Northern Pacific, or to save the great Australian cities from fleets stationed at San Francisco or New Caledonia?

[...] it would put an end to what a Canadian statesman describes as “colonies cutting each others throats with razors called tariffs”. It would create between us an intercourse of mind. [...] It would result in the creation of a national spirit [...] And, finally, it would give Australia complete control of her own resources for the protection of her own interests.

Alfred Deakin, an eyewitness to, and key participant in, the process of federation, wrote in his ‘The Federal Story’ (based on notes he kept during the years that federation was discussed and progressed):

The Federal impulse of 1880 was in the first place a reaction from the ultra-Protectionist policy [of the Victorian colony] of 1878-9 some of whose imposts, and the Stock Tax in particular, being directly aimed at intercolonial imports, naturally provoked great bitterness on the border.

In this, he wasn’t far wrong. After the idea of federating had floated in the ether for years and decades, and an abortive start toward Fedaration was made in 1890, matters finally came to a head in 1893 when people around the Victoria-New South Wales border gathered in a meeting which later became known as “the Corowa Conference” to push for action on federation because they were sick and tired of paying customs every time they moved goods across the river.

Back to Deakin’s ‘Federal Story’:

Dread of German aggression in New Guinea and of a French annexation of the New Hebrides [was among] the chief operating causes of [the Intercolonial Convention of 1883].

Deakin himself said:

... that they [the Australasian Colonies] were asked [by the British government] to surrender the New Hebrides as of little commercial value and in the next breath were told that the French set the greatest store by them for commercial development. [The French’s] interest in Australasia were spoken of as large, while ours which were incomparably larger were brushed aside as of no account. [...] We were assured that our alarm as to French intentions was groundless but we should never forget that it was while relying on a similar assurance from the Colonial Office, our trust had been betrayed by a surrender of part of New Guinea to Germany.

So, intercolonial taxes and mutual defence were two of the main issues.

Henry Parkes, the so-called “Father of Federation” repeatedly stressed the issue of mutual defence, starting with his Tenterfield Oration:

The Imperial General who inspected the troops of the colony had recommended that the whole of the forces of Australia should be united into one army. It would be pleasing if they could rely on being safe without taking military precautions at all; but as this was impossible, they must take measure to defend themselves

The Australian Natives’ Association, a mutual society exclusively for Australian-born natives (of British descent, of course!), was strongly in favour of Federation. They were behind the previously mentioned the Corowa Conference. They also believed:

[...] the future well-being of Australia, its progress and prosperity, and the material wealth of the colonists themselves, depend on its being united.

[...] the Board of Directors [of the ANA] must organise a crusade throughout the length and breadth of the continent [...] The great body of native-born electors in the Riverina should be aroused to a sense of the possibilities that may follow their co-operating with brother Australians. [...] inasmuch as the Board considers the people of Australia, from the Gulf of Carpentaria to the Australian Bight, and from Perth to Port Jackson, want to be appealed to, they recommend the [ANA] Conference to instruct the incoming Board to open a vigorous campaign. The time is ripe for an appeal to the whole of Australia.

[Report of the ANA Conference at Warrnambool, Victoria in 1894]

But, regardless of the ANA’s call to co-operation and brotherhood, the main two reasons the Australian colonies federated were to remove intercolonial taxes and mutual defence.

Scotland, Ireland and Wales along with England were all integral parts of the UK with full representation in the UK government. The four nations each benefited from the Union, for the most part anyway. And so with the exception of Ireland, there has never been a majority in any of the four in favour of independence. (that may change soon though.)

Canada, Australia, New Zealand and others were possessions of the UK. They didn't not have representation in the UK government. Instead they had their own system of government headed by a Governed General who represented the Queen. They were, to a great extent, independent from the UK on many matters already prior to official independence. These territories had developed to a level where they could look after their own without the British to assist and so more extensive independence was beneficial to them and freed the British of the costs of maintaining garrisons in far flung corners of the globe. Particularly after WWII when the British were rather strapped for cash.

In addition, post WWII there, the anti-colonial movements were gaining ground and a lot of political pressure was placed on the British government to make states independent of the empire (wither they wanted it or not). This anti-colonialism applied to Ireland too as it was seen as a colony, but did not apply to Wales and Scotland, and certainly not the England, as they were, as I said before, integral parts of the UK and closely bonded together with a single government.

Canada, Australia and New Zealand are however still lightly connected to the UK through the British Commonwealth. All the Commonwealth nations share the same Queen as head of state and they each still have a Governor General who represents the Queen in those countries.

Conversely, Ireland left the Commonwealth shortly after gaining independence and so is today completely independent.

Australia achieved independence from the United Kingdom in 1986 ( http://en.wikipedia.org/wiki/Australia_Act_1986 ). This occurred for a number of reasons: The UK's entry into the EEC and the exclusion of Australian exports from the UK market; Lingering resentment over the nature of the Dismissal; and, the fact that Australia had been a functionally self-governing advanced industrial nation since 1901, and that this was the final conclusion.

Australia federated in 1901 to eliminate internal customs barriers, and to ease local responsibility for imperial self defence. This heightened the attempt to produce an Australian manufacturing economy, and new found Federal powers were used to supplement existing initiatives in this area.

Australia developed a manufacturing economy because of the distances involved in transport, and the poor supply of goods from the UK. As soon as this began, Australia developed semi-independent capital. From this point onwards the idea of the United Kingdom maintaining permanent administration over the Australian colonies was a fairytale. I'd suggest looking into the development of Australian Liberalism in the 19th Century, and its defeat of the squatocratic conception of a "status society" in Australia. With Australian Liberalism came the Australian Bourgeoisie (a local version of the UK outfit), and with such localisation came the idea of a manufacturing economy.

I'd suggest Raewyn Connell, Terence H. Irving (1980) Class structure in Australian history for this, it goes into a number of decisive points in the replication of Australian class society and its economy.

Simple answer - it's complicated!

The world was very different in 1776 than it was in 1867 or 1900. The US war of independance followed the movement/ideas that led to the French revolution and was a real political/philosophical difference in how you should run a country. It was also concentrated in a few large cities with a large established political class. At the same time Canada, NZ and Australia were much more sparsely populated by people who were mostly much newer immigrants and still thought of themselves as British so there was no real 'independence' movement.

The formation of these three into separate countries was a much more gentle gradual process and generally fairly peaceful. I think there was a genuine feeling that their economies, population etc was big enough to stand on their own and there was no legitimate reason to stop them - better as friendly 'cousins' than prisoners.

India, the remaining bits of Africa and the Caribbean following WWII was more a combination of, "we can't afford them", "we just fought a war for freedom we can't really justify our own Reich" and the Bomb+Cold war makes the empire pretty irrelevant anyway.

Why Scotland, England, Northern Ireland and Wales didn't get separated then?

At the time? Because either their economies and population didn't support it or were much much more interlinked with England's. Ireland is a bit of a special case - there were political/religious reasons for it being independent which overrode other concerns