What international challenge was the most important for the United States to move the country and other countries forward after the war?

Solving economic matters by promoting international trade.

Trying to prevent the Communist governments from rising in European countries.

Promoting international peace.

All of the above

I could be wrong, but it could be all of the above. The US was pumping billions of dollars into war-torn countries to recover economically to be able to trade goods, like how they pumped money into Japan and it recovered almost instantly and began to trade goods with the US that continue to this day. Don't forget that the world powers after the war created the UN to promote international peace, alongside other things. Although trying to maintain peace, the Soviet Union is closing itself off from the Western world by infiltrating neighboring countries and overthrowing their government and installing a Soviet communist-style government. Winston Churchill is fearful of this and gives a speech about it in Fulton, Missouri in which he says that Stalin has put up and iron curtain. In response to this, the US enacts a containment policy, to stop the spread of communism.