On this day in 1607 English colonists arrived at Jamestown. This settlement, not the arrival of the Pilgrims at Plymouth, was the founding of the first successful English colony in North America. Over at Cliopatria, historians discuss why the Puritan separatists and not the Jamestown pioneers have become enshrined in our national memory as the founders of America [here]. For more information on Jamestown and the current round of celebrations go [here].
On this day in 1846 the United States of America declared war on Mexico. This war established American dominion from "sea to shining sea" and precipitated the crisis that brought about the Civil War. For more information go here and here.