I'm pretty sure the Foraker act.
Answer:
Slavery was against Mexican law, but Americans brought slaves to Texas. Many American settlers and Tejanos, or Mexicans who lived in Texas, wanted to break away from Mexico. ... After this, Texans declared independence and formed the Republic of Texas. Sam Houston led their army in a surprise attack at San Jacinto.
Explanation:
Abundance of resources = trade/cooperation
Scarcity of resources = conflicts
The more resources you have the more likely a civilization was to get along with those around it, although at the same time if the civilization was weak and had a lot of resources it would be at risk of invasion/attack.
US military lifts the ban on women in combat for Iraq and Afghanistan