“This isn’t America’s fight.”
Precisely what the French government said about Czechoslovakia in 1938. France and Czechoslovakia had a mutual defense agreement when France refused to uphold.
Britain was even worse. Winston Churchill was horrified, but he had made himself so obnoxious over the preceding decade that nobody cared what he thought. (In particular, he had fought to keep the Nazi sympathizer Edward VIII on the throne!) At least the Labour Party leader Clement Attlee spoke out:
“The Prime Minister has confidence in the good will and in the word of Herr Hitler, although when Herr Hitler broke the Treaty of Versailles he undertook to keep the Treaty of Locarno, and when he broke the Treaty of Locarno he undertook not to interfere further, or to have further territorial aims, in Europe. When he entered Austria by force he authorised his henchmen to give an authoritative assurance that he would not interfere with Czechoslovakia. That was less than six months ago.”