Also the sudden collapse of the Soviet Union, which presented both an unexpected opportunity and a risk. Opportunity in that Russia was no longer the enemy and

Also the sudden collapse of the Soviet Union, which presented both an unexpected opportunity and a risk. Opportunity in that Russia was no longer the enemy and could be a partner with experience running space stations. Risk in that Russia was not going to spend as much on space by themselves as the Soviet Union did, and their rocket engineers might have been tempted to go work for Iran, North Korea or other countries with nuclear ambitions. By doing the ISS together with Russia, those engineers were kept employed.