Poland signed Non Aggression pact with Nazi Germany in 1934.
Soviet signed neutrality pact with Japan in 1941. It was proven a successful strategy.
I was thinking of the Molotov–Ribbentrop Pact, in which the two leftist tyrannies agreed not to go to war with each other.
After the pact was signed, the American Communists (and other assorted useful idiots) were all complete and total non-interventionalists, marching outside the White House to stay out of the war.
Then, when Germany invaded the USSR, in a heartbeat...literally...they switched as if on demand to agitating for the USA to get into the war.
That was what I was referring to...