The specific timing on your allegations is off. A lot of the IP theft occurred in peacetime. The US and UK were at war for a total of like 11 years, and there was a period many decades of IP theft. It wasn't as state sponsored as it was during the period between the two wars, but it still happened.

Hell as late as 1850 the US straight up didn't recognize copyright of non US citizens. I forget exactly when that changed.