In 1812, the USA invaded Canada as part of the British Empire. The British fought them off. That was the last time any country invaded today's Canada with a military force.
In 1837 the internal Lower and Upper Canada Rebellions were defeated by British forces.
In 1865 an Irish gang the Fenian Brotherhood arose on the border with the USA, but the USA worked just as hard to control them as Canadians did. However, there was a real invasion threat then, of USA expansion up the west coast. It was defeated, not by arms but by the brilliance of John A. Macdonald, who espoused and worked out how to build the transcontinental railway from both ends at the same time, thus actively involving British Columbia in joining Confederation, to dissuade them from joining the USA.
In 1885, 5,000 Canadian militia were sent to Saskatchewan to crush the North-West Rebellion.
Ever since, Canadians have fought other nation's wars.
Until 1931, the Statue of Westminster, Canada was considered a colony of Great Britain, so automatically took part in British wars:
- In 1884, Canada fought the Mahdi of Sudan along with British forces.
- In 1899, Canadian forces joined those of Great Britain to defeat Boer independence in South Africa.
- In 1914, Great Britain declared war on Germany, thus involving Canada. Although called a "world war", it was in fact solely a European conflict.
- In 1919, Canada joined British troops in Siberia to aid the White Russians in the Russian Civil War.
After 1931, as an independent nation:
- In 1939, Canada declared war on Germany out of loyalty to Great Britain, although no longer required to, and defended British interests in Europe and Hong Kong.
In 1941 we also declared war on Japan, again in concert with Great Britain, after Japan's attack on Hong Kong.
- In 1949, Canada joined NATO thus actively involving ourselves in unifying Europe and fighting the expansion of Russian influence.
- In 1950, we joined with NATO in fighting the 'commies' in Korea.
- From 1948 to 1991, as a member of the UN, Canada sent armed "peace keeping" missions to Kashmir, Cyprus, the Sinai and Golan Heights, Bosnia, and Somalia.
- In 1990 an internal revolt by Mohawk at Oka was defeated by Canadian militia.
- In 1991 we defended Kuwait against Iraq.
- In 2001 we took sides in a conflict in Afghanistan.
150 years after Confederation, there is still no external threat to Canadian territory.
We still maintain armed forces, but only spend 1% of our GNP on them.