You need to look at the national interests of the Allies, the Central Powers, and the US. Essentially, the Allies were the "haves" of the world, they dominated the existing international system. They had control of world finance, world trade, and the largest colonial empires. The Central Powers were the "have nots" that challenged the international system in order to create a new one where they were dominant.
That was what was at stake. Would the world continue to be dominated by Britain and France? Or would the world be based on a new international order based on German control of Central and Eastern Europe?
Now, what are the US interests? First, it enjoys a lot of advantages in the current system run by Britain and France. Like the US, both are representative democracies. Neither threatens the US homeland. Much of the previous animosity towards Britain has ended in the past several decades, and the US still has a very favorable opinion of Lafayette's homeland. The current economic system offers a lot of advantages to the US whose own economy is similar. It has no intention to expand its colonial empire, although it wants to retains its dominance in the Western hemisphere. Under these circumstances, the US does not have many reasons to want to overthrow the current international order.
At the same time, it is not entriely clear that an order based around Germany would be very bad. There are concerns about its lack of democracy, and the US would not be served by a Europe dominated by any one power. Thus, there is a slight interest in preventing a Central Powers victory.
In order for the US to want to join the Central Powers, you need to give it a strong reason why a Central Powers victory is in their best interest. You need a much more anatagonistic relationship between the US and Britain/France. This would involve a POD of several decades before WWI. You also need a Germany whose politics could be seen through American eyes as being more favorable to the US depsite its democratic deficit. One possibility is Germany being far sighted enough to make an issue of the "captive nations" in Europe by Britain (meaning Ireland) and Russia (meaning Poland and some other lands). This, of course, will be very hard considering Austria-Hungary and its own ambitions in the Balkans.
So this requires a very different world than the one we have in 1914. It's possible one could be engineered so, but the national characters and interests of each country naturally propel the US to be sympathetic to Britain and France, not Germany.