The correct answer is:
President Theodore Roosevelt won the Nobel Prize in 1906 for the Treaty of Portsmouth.
Explanation:
1. The Treaty of Portsmouth refers to the treaty that ended the Russo-Japanese War in 1905. President Roosevelt played a significant role in mediating the peace negotiations between Russia and Japan, which ultimately led to the signing of the treaty in Portsmouth, New Hampshire.
2. His efforts in brokering the peace agreement were recognized internationally, and he was awarded the Nobel Peace Prize in 1906 for his successful mediation in the conflict.
Therefore, the Treaty of Portsmouth is the specific reason for which President Theodore Roosevelt won the Nobel Prize in 1906.