Wikipedia can be a good starting point for finding information online, but the anonymity of the site can lead to unreliable information. The online version of Encyclopedia Britannica is a much better option for reliable background information on the web. Here are some of the most recent entries from the site:
General Encyclopedias are a great place to start getting basic information on a topic.
In order to present a strong argument you need to know as much information as you can on the background of your topic. Before you begin searching, stop and think about what kind of background information will be most useful to you. Try making a list of questions you need answered about your topic. For example, if you are writing about a recent decision by the supreme court you might ask yourself -
Your background research will often involve getting information on more than just the topic itself.
One of the best places to look for background information is in the library's research databases. Here you can find a lot of general information on a variety of topics.
Encyclopedia focused on a particular subject will often cover their topics in greater detail than general encyclopedias. If you aren't finding what you need in one of the library's general encyclopedias try search the library catalog or the Credo Reference database for a reference book on a particular subject.