What was Christopher Columbus' main accomplishment?

Christopher Columbus' primary accomplishment was claiming America for Spain. Columbus was not the first European to sail to America--this accomplishment belonged to Leif Erikson, a Norse Viking--but his discovery of America in 1492 provided Spain with vast natural resources (gold, silver, sugar, etc.) and wealth. This wealth helped Spain build a huge army and navy (the Spanish Armada) and become the most potent empire in the world.

Columbus, of course, had not set out to do this. Rather, he had intended to find a western trade route to India and the Spice Islands of the East. He initially believed he had found India (hence the Spanish referred to the natives as Indians), but people slowly realized he had actually found a new continent.