It's supposed to be more difficult than a high school class; that's what we signed up for.
The problem is that we're trying to take the equivalent of a college history class in 45 minutes a day. So, yeah, outside research is necessary.
And don't knock wikipedia.
Dinnertime. 
Considering that a college history class is going to be 50 minutes for five days a week (assuming 5 credits and a quarter system) it's a case where let's face it high school academics are... well a joke.
Sure, outside research is necessary in college but you also don't have the load of busy work that High School (even Honors or AP classes) have.
Of course part of the issue is the whole parents being convinced "are our childrens learning" doesn't happen unless they're constantly busy. Half of the time even the low-work load of some lower division college courses could be cut down. (an actual research paper or two per quarter or a research project instead of drowning in smaller assignments)
In the end, most education needs a leaner 'smarter, not harder' approach. Instead of long assignment regurgitating the text, giving people actual skills to look up original sources and know how to use them is more valuable for college prep. (instead of having to teach it to every single intro course over and over again when they're already supposed to know this...)