Why did europeans send expeditions to North America?

After Marco Polo brought back the things from Asia and wrote a book about his adventure the trade for goods from Asia was wanted by Europe. The only route was over the Silk Road which was long, dangerous, and costly. Shipping technology began to be developed which opened the door for seeking a water route to Asia. The man or nation that found it would be very rich. The finding of North America was an accident and it was far larger and richer in resources than they expected.