cold war
when reagan swept into the white house he wanted to win the cold war. hot war wasn't really a viable option. peace treaties weren't doing very well either. so what's left? undermine the soviet economy. it's tiny compared to ours. yet they could afford to match our icbm buildup by selling expensive oil. so reagan convinced saudi arabia to flood the market with cheap oil. the soviet economy tanked. and ours went gangbusters. end of soviet union. end of cold war. and as a bonus reaganomics (ie tax cuts for the rich) looked brilliant.