From the book "What do we know about war?"
1. Territorial disputes are far more likely to lead to war than other disputes. This is probably because such disputes are highly visible, don't give much room for policy maneuveuring, and lend themselves to military fights (since armies are designed to capture ground)
2. Alliances have generally led to increased war, but there are fundamentally different kind of alliances. An alliance between Peru and Ecuador to take over Europe doesn't really matter. Similarly, a non-aggression pact between France and Germany because they just settled an old dispute generally does not lead to increased violence. On the other hand, an alliance between two unhappy states, or states that have a big difference in power, lead to war. The first because neither country likes the status quo, and the second because states generally do not ally with other states that have more power or less power than them...a new alliance would imply war soon.
3. Democracies behave differently. They make alliances for non-strategic reasons, ally with other democracies, have longer alliances, and escalate more when facing non-democracies.
4. Military buildup increases the chances of conflict, especially when the international order is in flux and when the defense budget is high.