I believe that injustice is the primary impulse for conflict. However, this can also include:
Unmet needs: I think that unmet needs, such as access to food, health care, social justice, primary education, and proper housing, can and have already fueled conflicts on all levels. If a family, a city, or an entire nation does not have enough support from the governments or actor actors, situations tend to escalate at one point. Crime rise, protests increase, which can develop into a regional crisis or civil war. 
Resources: Resources, such as water, oil, gas, or minerals, can in times of globalizataion, and rising demands attract international interests. However, resources can also lead to national conflicts or community conflicts. Resources can mean power and create an imbalance of power under which communities can suffer. Often related to resources is also greed as an underlying motivation.