The first half the 20th century was a race for power, the entirety of Europe was paranoid, relationships in the form of treaties were created to ease the stress on particularly weaker countries (Example would be Russia at the time and Austria Hungary). There is a lot of debate if World War 2 was caused due to a long term cause or a short team cause, I believe it was a mixture of both ;On the 28th of June 1914 Franz Ferdinand was assassinated by the black hand gang (a Serbian gang), this leads to Austria Hungary declaring war on Serbia, Russia moves troops in to Serbia to help, but later on Germany accuses Russia of mobilizing and declares war on Russia numerous European countries declare war on each other and World War I began.
Africa was also a big factor leading up to the events to World War I ,prior to WWI a lot of European countries began to colonize in Africa , because Africa at that time had great potential for providing a lot of resources for those European empires to expand and could've easily increased military power. A lot of tension arose and one of the most noticeable results was the Moroccan Crisis (1905-1906). Morocco was an uncolonised African country that France wanted as part of their empire, however Germany at the time wanted to expand their empire and German influence around the world and wanted Morocco for themselves so they objected to France taking control over it; a international conference was called which in the end lead to Germany backing down and letting France assume control of Morocco. This is a perfect example of the race for power in the 20th century , and Africa being a cause for WWI. The first two Balkan wars were also contributing to factors to the short term cause of World War I, Serbia wanted the Slavic people to be free and not under the control of Austria Hungary, In 1908 Austria Hungary