The first effect was to enlarge the diet. The main effect; was American Food could feed a family on a small area of ground, took a couple of hundred years to get around. Kinda brings us up to the End of the Little Ice Age.
Yup. (Little Ice Age, 1300-1855). The potato was imported to Europe from the Americas. Note the effect on the Irish of the 1850's potato blight in Ireland, 1.5 million starved and about the same number survived by immigrating to America.
The September front page article of Discover magazine explains how we could slip into another Little Ice Age as soon as two years from now.