Geopolitics is an interest in or taking of land for its strategic location or resources. England was interested in India for its location and resources native to that area.
The Berlin Conference was a meeting between 14 European nations to discuss how to divide African land. This meeting was held between 1884-1885, and it did not include a single African leader.
The Boer Way or South African War was the first modern "total" war between the British and the Boers over land in South Africa.
The Ottoman Empire falls because it had a weak set of rulers. Weak rulers caused various other issues such as financial loses and inflation.
The Crimean War occurred when the Russians attacked the Ottomans because they wanted the land around the Black Sea. The British and the French entered the war to help the Ottomans because the Ottoman Empire was too weak to fight the war on their own.
Imperialism is when a stronger country/region takes over a weaker country/region because they want land, money, resources, and to show dominance and/or power.