Final answer:
Spain and Portugal were the two countries that primarily raced against each other in the 1450s to explore new lands, leading the European Age of Discovery.
Step-by-step explanation:
The two countries that raced against each other to explore new lands beginning in the 1450s were Spain and Portugal. This era is known as the European Age of Discovery. These two Iberian nations led the way in exploration due to their advantageous geographic positions on the Atlantic Ocean, technological advancements, and a desire to expand their kingdoms through trade and colonization.
Detailed treaties like the Treaty of Tordesillas and the Treaty of Zaragosa alleviated competition between Spain and Portugal by dividing the world into two zones of influence. This division allowed for a more organized spread of their respective empires. While other countries like England and France also had ambitions of overseas expansion, they lagged behind and had to deal with internal conflicts before they could fully participate in the Age of Discovery in the seventeenth century.