This video shows the European expansion starting from the 15th century. Portugal actually begins exploring the oceans before that date. 

It is important to understand what the sea meant for commerce and trade after 1453. Remember that important date! 

The Treaty of Tordesillas divided the world in 1494

The Treaty of Tordesillas was ratified by the Catholic Monarchs in Arévalo on July 2, 1494, while King John II of Portugal did the same in Setúbal on September 5 of that same year. The Castilian version is preserved in the National Archive of the Torre do Tombo in Portugal, while the Portuguese version is kept in the General Archive of the Indies.

The treaty established the limits of navigation in the Atlantic Ocean, as agreed upon between the Catholic Monarchs and King John II of Portugal. It set a new demarcation line 370 leagues west of the Cape Verde Islands, assigning the western half to Castile and the eastern half to Portugal. Both parties agreed not to cross or explore beyond their respective limits, respecting the boundary established by the treaty. This agreement ended the disputes arising from the division of newly discovered territories following the arrival in America in 1492.