【Alliance】 , 【League】 , 【Coalition】 , 【Fusion】 , 【Confederacy】 , 【Confederation】 and 【Federation】 all agree in the idea of combination, chiefly political, for a common object.

【Alliance】 applies particularly to a joining of interests on the part of families (by marriage) or of states (by compact or treaty); it is also less formally used of a connection for mutual benefit between other bodies, organized or not.

• a defensive 【alliance】
• an 【alliance】 between producers and consumers

【League】 though often used without distinction from 【alliance】 typically suggests a more formal compact or more definite object and may frequently (unlike 【alliance】 ) be taken in a bad sense.

• the Solemn 【League】 and Covenant
• to be in 【league】 with the powers of darkness

【Coalition】 refers to a temporary 【alliance】 of otherwise opposing interests, parties, or factions.

• Mr. Fox, and his famous 【coalition】 with Lord North
  —Gibbon
• a 【coalition】 government

【Fusion】 is a 【coalition】 of political parties for the purpose of defeating another party in an election.

• a 【fusion】 of Republicans and independent Democrats in New York City opposed the Tammany Democratic ticket

【Confederacy】 and 【confederation】 apply specifically to a union by compact or treaty of independent states under a government to which powers are delegated for dealing primarily with common external relations.

• the Southern 【Confederacy】
• the Articles of 【Confederation】
• the German 【Confederation】

【Federation】 in its broad sense includes any union under the terms of a 【league】 or covenant but specifically it designates a sovereign state or city formed by the union of other states or cities with a central general government and several local governments.

• the 【Federation】 of Labor
• the United States of America constitutes a. 【federation】
• 【federation】 was the name given to the scheme for blending the Five Towns into one town
  —Bennett
• the 【Federation】 of Malaysia