This was due to the US seeing how the "punish the losers" strategy after WWI led directly to WWII and us trying not to repeat that same mistake after WWII (sort

This was due to the US seeing how the "punish the losers" strategy after WWI led directly to WWII and us trying not to repeat that same mistake after WWII (sorta kinda, there was more at stake, such as the Cold War, which helped shift alliances also). But basically the US decided helping the people who lost the war reconstruct can keep our influence in the area and reduce the desire to rise back up and retaliate against them. The US actually tried exactly this same approach after the Afghanistan and Iraq wars (remember all the money spent on rebuilding afterwards, training police forces, etc?), and it turned out to not work out so well for them this time around.