The last session of the League of Nations occurred on April 18, 1946, during which the member states passed a resolution for the dissolution of the League. This marked the formal end of the League of Nations as an international organization. The dissolution was a result of the League's inability to prevent World War II and its diminished role in the post-war world order. The functions and responsibilities of the League were largely taken over by the newly established United Nations (UN).

The World Health Organization (WHO) was founded on April 7, 1948. The WHO's constitution was adopted by the International Health Conference in New York in 1946. The WHO is a United Nations specialized agency. 

The famous treaty between Russia and Napoleon in 1807, which contributed to Napoleon reaching the peak of his height, was the "Treaty of Tilsit." Therefore, the correct answer is:

(C) Treaty of Tilsit

The Peninsular War took place from 1808 to 1814 on the Iberian Peninsula. It began when Napoleon invaded Spain and Portugal. Widespread resistance from Spanish and Portuguese forces, along with guerrilla warfare, led to a protracted conflict. The war significantly weakened Napoleon's forces and contributed to his strategic challenges. The conflict ended with the defeat of French forces in the region by the Sixth Coalition, consisting of British, Spanish, and Portuguese allies.