Because humans nature has not and will not change. There is nothing new under the sun. Humans are the same. Some are good some are bad. The bad ones look for opportunites to cause trouble.
Weakness invites aggression.
Strength yields peace. America has long upheld free trade among nations. Look what has happened in Mexico, the Four Tigers, and other emerging markets. Jobs are flowing into those markets. Last time I checked the United States was the world's leader in pursuing human rights abuses among the world's nations.