Answer:
The most successful European country at conquering the Americas and spreading their culture in the early 1500s was Spain.
This was due to their advanced naval technology, superior military forces, and the establishment of the Spanish Empire.
Spain was able to establish colonies in many areas of the Americas, including Mexico, Peru, and parts of Central America, which allowed them to spread their culture and influence to the region.
Additionally, Spain was the first European country to establish permanent settlements in the New World and to explore the Pacific Ocean.