I assume you mean the war started, but then we have an early negotiated peace. IMO, this has to happen when the fronts are relatively stable, so this means over a winter. I also assume you are not changing the outcomes of battles. Unlike carlton bach, I don't see it being ended before the winter of 1915 and 1916. The fronts are very fluid, and at any given time one sides looks like it is just another major push from victory or a better place to negotiate peace from. First the Germans have success in France, but this stalls. Then the Russians lose 1.5 armies to the Germans. Then the Russians take the two major A-H fortress cities and look like they are about to break into the central Hungarian plain. Then couple months later, the Germans counter attack, and it looks like Russia is collapsing. Finally by September 1915, the fronts look stable. To have peace in this time frame, means the winner must have a very generous offer to whoever looks like it is losing in a given month. This implies a prewar plan to do this, since coming up with an offer is a complicated internal issue for even one power, much less a coalition. If you get a peace here, I think you guarantee a stabbed in the back myth (perhaps a lot of truth to this one), and a second war, probably faster than OTL. This is an ugly scenario with much bigger armies fighting part 2 probably in the late 1920's. There has not been enough suffering to drive the needed changes.
Now over the Winter of 1915/16, there are starting to begin to see calls for peace. The front is fairly static for about 6 months. With the right mediation (Wilson is effective agent for peace, Pope gets heavily involved), I can see it being done. So what does a peace deal look like.
1) Minor symbolic reparations.
2) Either minor colonial adjustments or status quo prewar, excluding what Japan takes.
3) Poland ends up as some type of neutral buffer state or DMZ. Belgium goes back to neutral status.
4) The western Front is more of an issue. France wants A-L. Germany wants to keep it gain, so I guess we go back to status quo prewar. At this point, Germany has feels it is winning, so it has given up a lot. It needs something back, and I have trouble seeing where this goes. Maybe some colonial concessions such as French Equitorial Africa is enough to make it workable for all sides.
Now what do we get here. Probably enough suffering to get people to accept, but we still have stabbed in back issues. Russia will have another deep crisis like after its war with Japan. A Polish buffer state will help both sides, but will be hated by both German and Russia. France will have suffered greatly, and will be fearful of future. It has to keep its large army, and builds some type of massive defensive line. Naval race continues, we see the 17" guns. UK will need to keep a large standing army, and likely does due to strategic realities. USA stays much more isolationist, but does build large navy. We end up with a lot of European countries that are poorer than prewar, and this causes stability issues. A-H can go a lot of ways. Italy will feel betrayed.
But don't get me as too pessimistic. The worst of the Great Depression is avoided. The demographic issues are largely avoided. Europe still exports a lot of people, but less than prewar. Algeria is still a part of France,and is majority Christian. As is Libya. Tunisia could well be in this category. A lot of African colonies and South America are whiter.
You asked a pretty broad question. Is there some area you are more interested in. It basically butterflies away OTL, so we could write thousands of pages on the topic.