Which causes were responsible for the rise of middle class?

The causes responsible for the rise of the middle class were :

• In the crusade, a lot of feudal lords had been killed.
• The growth of commerce and trade made the trading class quite rich and prosperous. They, in turn, sought the favor of king and helped him, whenever needed.
• The wealthy merchants and rich traders got many towns and cities freed from the clutches of feudal control.
• The new cities soon grew into centers of trade, commerce and education and consequently gave rise to the new classes.
• New classes of the rich merchants patronized art, science, literature and education.