Provide Context for the Argument
The introduction establishes an argument's context: it informs the audience of the issue at hand, the prevailing arguments from opposing sides and the position held by the author. It sets the tone for the argument and establishes the disciplinary constraints and boundaries that your particular academic audience will expect.
There are many ways to provide context for an audience but the main thing is to get everyone on an equal footing, a starting point where everyone has equal knowledge of the issue.
One of the best ways to accomplish this is by proposing a common definition of the issue. Another is to begin with a literature review of past work, showing where and how your position has emerged from previous work and how it enters into or contributes to that conversation.