In an introduction to an essay, the most important element is the thesis statement. You should also include a definition of human trafficking.
When writing an essay on any topic, the most important element is the thesis statement. A thesis statement is one sentence that directly addresses the prompt and explains what you are going to be writing about.
You need to find a direction to go with a broad topic like human trafficking. You can discuss causes, legal approaches, effects on those involved, or some other direction. The direction you choose should be clear in your thesis statement.
Another important aspect of an introduction for a paper like this is a definition. You need to include a definition of human trafficking. Get your definition from a trusted source. Here is one from the United Nations Office on Drugs and Crime.
It involves an act of recruiting, transporting, transfering, harbouring or receiving a person through a use of force, coercion or other means, for the purpose of exploiting them. (www.unodc.org)
Now your introduction has a thesis and a definition. You can put those in any order. You also need some kind of hook. A statistic is a good place to start. You can also choose an anecdote and tell a personal story, not necessarily yours but of someone affected by human trafficking.