The Port of Baltimore in Baltimore, MD on Thursday, Oct. 2, 2014. The Port of Baltimore is one of many ports in the U.S. involved in agricultural trade. U.S. and global trade are greatly affected by the growth and stability of world markets, including changes in world population, economic growth, and income. Other factors affecting agricultural trade are global supplies and prices, changes in exchange rates, government support for agriculture, and trade protection policies. Diversity in consumers' food choices and changing relative exchange rates, make U.S. goods relatively more/less expensive in international markets and import goods relatively less/more expensive. USDA photo by Bob Nichols.