The option that most directly contributed to peasants' inability to build wealth is:
2) Peasants were required to tithe 90 percent of what they earned to lords.
High tithes would significantly limit the amount of wealth that peasants could accumulate, making it difficult for them to save or invest in their future. Options 1, 3, and 4 do not directly address the primary issue of wealth accumulation in the same way that high tithing does.