What Were the Causes of World War 1 - Main Causes of WW1

At the turn of the nineteenth into the twentieth century, capitalism crossed in the monopoly stage of its development.  One of the major features of this development was the association of capital and production in large companies or monopolies.  This was used by the major European countries (England, France, Russia, USA etc..) to perform division of world markets and territorial areas or colonies. Thus, they became colonial empires and drew large revenues from their colonies. Countries that later carried their union in the nation-states (Germany, Italy, Japan, etc.) could not enter to these colonies and markets, which affected their interests for profit and gain.
These unsatisfied countries tried to perform a new distribution of the colonies as a source of raw materials, income and cheap labor world markets, and to initiate a new division of the world.
According to their interests, major countries began to cluster around two conflicting sides to create two alliances of states, not being able to peacefully carryout the division of new colonies and distribution of markets.
One countries trying to maintain their position and others threatening to change this, both sides started to prepare for war.
One block of states, known as the Entente or Allies consisted of France, Britain, Russia and later joined Serbia, Italy, the U.S., Romania and others. This block endeavored to keep the already gained allocation of countries and strategic interests in the world.
Later created nation states in Europe, joined their interests in the so-called Triple Alliance or Central Powers block, consisting of Germany, Austria-Hungary, Bulgaria and Turkey.
As the occasion for the beginning of the war, served the Sarajevo assassination of Archduke Franz Ferdinand of Austria, on June 28, 1914.

Archduke Franz Ferdinand with his wife Sophie, Duchess of Hohenberg (Ратни албум 1914-1918, Поповић, Андра, Београд, 1926)

Arrest and trial of Gavrilo Princip and his accomplices (Ратни албум 1914-1918, Поповић, Андра, Београд, 1926)

One month later Austria-Hungary backed by Germany, declared war on Serbia, knowing that the attack on Serbia, due to Russian interests in the Balkans and charged international relations, will cause a general war.

"The Chain of Friendship", an American cartoon from 1914 erroneously depicting the supposed web of alliances, captioned, "If Austria attacks Serbia, Russia will fall upon Austria, Germany upon Russia, and France and England upon Germany."