Content... content... content...

And links to your forum from content related sites

Actually, overlapping content might be more preferable. If a civil war site exchanges llinks with a wwII site, you both might turn up in a search for war. If two civil war sites exchange links however, both are more likely to be ranked higher for the search term "civil war"

It's also a good idea to have content that contains your keywords on the home page. Metatag keywords are not used much anymore. Search engines like to use bayesian filters on page content. Basically what that means is that for any given topic, certain words are often found together on high ranked pages.

So for a civil war site, they might expect that early (first thing on the page) page content might contain the terms civil war, grant, lee, lincoln, gettysgurg, etc.
The theory is that them more topic-related terms on a page, the greater the likelyhood that the page is of interest to certain search terms. Repeating the term "civil war" 10 times is less important that stating it once, and having 10 other topic related terms on the page. Note that 50k of javascript/embedded css is going to push your content lower down in a "view source" - which is how the Search Engines view your page.

Look at the highest ranked pages in your search term categories and see what they use for content. Also go into google and do a "link:www.theirhomepage.html" to see who links to them. You want links from those same sites.
Some pages have poor content but are highly ranked. Usually due to longevity. Pages that have been around for a long time get a boost, and usually have links pointing to them.

SEO is a moving target, the algorithm's change, but the engines want to serve links to pages that people want to go to so content is always king. People try to spoof the engines, but all that really does is stroke your ego and bring people to your pages who don't want to be there.