European contact with Africa increased during the 1800's because of the want for natural resources, land, and increased global power. European countries competed over territories in Africa, known as the "Scramble for Africa," right after the Berlin Conference in 1885.
This competition allowed for countries like Spain, France, Britain, and Germany to expand their political and economic influence. Once territories were taken over by these countries, they would exploit the resources found in different African countries and use them to benefit their country.
Along with this, industrialization was increasing rapidly throughout Europe. Due to this increase, the demand for raw materials and new markets (aka new people to buy materials) increased as well. All of these factors played a pivotal role in increasing contact between Europeans and Africans during the 1800's.
The United States placed nuclear missiles in "Turkey", causing Russia to place some in Cuba, which is what led to the Cuban Missile Crisis, since the missiles were well within firing range of the US.
Essentially, the United Kingdom, France and the Soviet Union all allowed Germany to pursue its expansionist goals. They believed that giving concessions to Adolph Hitler was better than trying to oppose him at that point.
In the case of the United Kingdom and France, their leaders signed the Munich Pact with Hitler in 1938, allowing him to annex the Sudentland in Czech territory as part of Germany. Before long Hitler went on to take control of all of Czechoslovakia and later would invade Poland, and the British and French found themselves going to war with Germany after all.
In the case of the Soviet Union, the USSR and Germany signed a non-aggression pact in 1939, promising they wouldn't go to war against each other. That essentially gave Hitler permission to invade Poland without worrying about Soviet opposition. But by 1941, Hitler was breaking his promise and pursued an invasion of the Soviet Union.
