Agricultural techniques like irrigation could other civilization expand its borders because they could use irrigation to

Irrigation was one of the main reasons why civilizations were able to expand beyond their borders. The reason was that irrigation allowed them to not be dependant on rainfall for agriculture, which meant that they could farm more efficiently.

This new agricultural pattern meant that towns started having surplus food. And surplus food contributed to population growth, which allowed towns to turn into cities, and these cities to have a significant population that could become soldiers and wage wars of conquests.

Additionally, the growing population required more land to settle and farm, and this made them interested in conquering other territories.

although the crusades failed to capture jerusalem, they had several major impacts on western europe. they increased the authority of the king: sometimes nobles died in battle without leaving an heir in which case the king got their land. kings passed taxes to pay for the crusades.