Noun
wedge - A piece of material with a thick end that tapers to a thin edge, used to split, support, or secure things; also something that forces separation or division between people or groups.
The disagreement drove a wedge between the two longtime friends, and they really didn't enjoy spending time together anymore.
injustice - A situation in which the rights of a person or a group are ignored, and they are treated unfairly.
The American Colonies felt that 'taxation without representation' was an injustice that, among other things, warranted a revolutionary war of independence against England.