Why at the beginning of the 20th century was humanity facing the threat of a world war?

At the beginning of the twentieth century, the situation was heating up around the world. It was a period of great changes both in the economy and in the politics of many countries. And it was these changes that led to disagreements both in the state itself and between different countries. At that time, between the most powerful countries – the Soviet Union, Great Britain, Germany, there was a very fragile illusion of peace. In addition, each leader from these countries pursued his own interests, which led far from peace.