Dual Alliance- A defensive alliance between Germany and Austria-Hungary, which was created by treaty on October 7, 1879
Triple Alliance - In 1882 it was expanded to include Italy. The three countries agreed to support each other if attacked by either France or Russia. 
Entente Cordiale- 1904 Britain and France signed the Entente Cordiale (friendly understanding). The idea of the alliance was to encourage co-operation against the perceived threat of Germany. 
Triple Entente- 1907 Three years later, Russia, who feared the growth in the German Army, joined Britain and France to form the Triple Entente. The Russian government was also concerned about the possibility of Austria-Hungary increasing the size of its empire. It therefore made promises to help Serbia if it was attacked by members of the Triple Alliance. 
Colonialism: the building and maintaining of colonies in one territory by people from another territory.
Imperialism: The policy of extending a nation's authority by territorial acquisition or by the establishment of economic and political hegemony over other nations.
Nationalism: There were two kinds of nationalism in 19th Century Europe:

(i) The desire of subject peoples for independence -
It led to a series of national struggles for independence among the Balkan peoples. Other powers got involved and caused much instability.

(ii) The desire of independent nations for dominance and prestige -
As the powers try to dominate each other in Europe, their rivalries may be regarded as one of the causes of the First World War.

Militarism: Militarism denoted a rise in military expenditure, an increase in military and naval forces, more influence of the military men upon the policies of the civilian government, and a preference for force as a solution to problems. Militarism was one of the main causes of the First World War.
Arms Race:   After 1871, the war atmosphere engendered by the secret alliances led to an armaments race among the powers. The...