Iran controls a string of proxies in Lebanon, Yemen and other places. Are you sure you're not forgetting that piece? When you write that we had 80 years of relatively peaceful times, you're glossing over that fact.
We haven't had a major conflict in 80 years. Little skirmishes all over the place, sure, but we've forgotten that significant wars between major powers used to be both terrible for everyone involved and also common. Our grandparents after WW2 decided to go a different path and created a largely rules- and trade- based international order that has largely kept the peace. We don't realize how good we've had it.
Absolutely, there's been no major conflict like this since WW2. The strategy shifted to proxy controlled damage in places not US, not Russia, not China, but the weaker states where there was some incentive for control (resources, geography, political alliance, etc). While not a big state (not since centuries), Iran was a proxy controller with the capacity to cause mayhem.