Answer: Look at the explanation below!
Explanation: The main reason was the expansion of the Ottoman Empire in 1453; they took Constantinople (Now known as Istanbul) From the Byzantine Empire, which finally ended the Roman Empire. The Ottomans were Muslim, and the Europeans were Christians. They didn't want to trade through a Muslim power which was a big deal as the religion played a huge role, so to find trade routes to Asia, Portgual sent explorers to find a new path to India. They did this by sailing around Africa to reach India. Christopher Columbus tried to ask the Portuguese to fund his expedition to find a route by sailing west. Still, it was denied. He then tried his luck with the Spanish, and they budged, and with Columbus sailing west, he would discover the new world. I hope this answer was helpful!