Thank you. I get so tired of people claiming that the laws of any another nation decide the citizenship status of an American.
Why wouldn’t Canadian law apply to those born on Canadian soil?
But what would you do if he had remained in Canada and got drafted into their army? A country's own laws apply in their own country. If a man cannot be claimed under another nation's laws, he cannot be made to serve in that nation's army.
That's too broad. What is correct is the laws of other nations don't determine the American citizenship of an American. But, other nations may (and do) claim citizenship of people who are "born (at least partly) American."
For example, the babies born here on birth vacations are deemed by some to be natural born Americans, eligible for the presidency, even though neither parent is a US citizen, and even though the child is removed from the US at a very young age (weeks or months old) and raised in a foreign country.
For those people, the US, and ONLY the US, decides their US citizenship. But their citizenship overall may be more complicated, and determined by a country other than the US.