Why was it difficult for Hitler to conquer the Soviet Union?

One of the most important reasons for this was poor strategic planning. The Germans had no satisfactory long-term plan for the invasion. They mistakenly assumed that the campaign would be a short one, and that the Soviets would give in after suffering the shock of massive initial defeats.

Explanation:

the  wilmot proviso  was designed to eliminate  slavery  within the  landacquired as a result of the mexican war (1846-48). fearing the addition of a pro-slave territory, pennsylvania congressman david  wilmot proposedhis amendment to the bill.