The Arab countries, principally Saudi Arabia, refused to sell the US and other countries oil due to our decision to help Israel restock military weapons after the Yom Kippur war. See link.
When most of the world was deeply affected by the 1929 Great Depression, the Mexican Economic Miracle (1930-1970) was taking place, allowing some actions such as the nationalization of the oil...
Many things have happened so far. Some are animals are dying or getting hurt, and oil is washing up on beaches. People are finding a lot of oil on Pensacola beach.