I'm writing this at my house in central Connecticut. Twenty thousand years ago, this spot was buried under a mile of ice.
About thirteen thousand years ago, after the ice thinned and retreated, plants swept over the bare land. They came from the southern United States, and they established the same kinds of forests and swamps that had grown in Connecticut in earlier periods between the Ice Ages.
But today, many of the most abundant plants around my house today come from distant continents--plants like honeysuckle. And Japanese barberry. And ground ivy. And the knotweed. And on and on: you can read a list of invasive plants in Connecticut