For the first question, the most significant consequence of the European partitioning and mandate system of Southwest Asia after WWI is:
A. The mandate system caused conflict in Southwest Asia because it grouped people together with vast ethnic and cultural differences.
This option highlights how the arbitrary borders drawn by colonial powers led to tensions and conflicts among diverse ethnic and religious groups.
For the second question, the Mandate System began after:
B. World War I
The Mandate System was established in the aftermath of World War I as part of the decisions made during the Paris Peace Conference in 1919.