Recall the achievements of portuguese explorers

Portuguese discoveries is the name given to the maritime exploration by the portuguese during the 15th and 16th  centuries. 

Some of those achievements:

João Gonçalves Zarco and Tristão Vaz Teixeira discovered Porto Santo island in the Madeira group
Gil Eanes sailed round Cape Bojador
Diogo Afonso discovered the islands of the Cape Verde group
Diogo Cão reached the estuary of  the Zaire
Bartolomeu Dias round the Cape of Good Hope and entered the Indian Ocean
Vasco da Gama led the first fleet around Africa to India, arriving in Calicut
Pedro Álvares Cabral discovered Brazil on his way to India
Returning from India, Vasco da Gama discoveres the Almirante Islands (Seychelles)
Fernão Mendes Pinto, Diogo Zeimoto and Cristovão Borralho, became the first Europeans to reach Japan

  the domino theory states that  if one country in a region came under the influence of communism, then the surrounding countries would follow in a  domino  effect.