Nepal was a constitutional monarchy till 2006. Let's understand this answer in detail:

Constitutional Monarchy:
A constitutional monarchy is a form of government where a monarch acts as the head of state within the parameters of a constitution. The monarch's role is largely ceremonial and symbolic, and the real power rests with an elected parliament or government. The constitution outlines the powers and responsibilities of the monarch, government, and other state institutions.

Nepal's Constitutional Monarchy:
Nepal was a constitutional monarchy until 2006. It had a king as the head of state who acted as a ceremonial figurehead. The king's powers were limited by the country's constitution, and the real power rested with the government and parliament. Nepal had a multiparty democracy, and the prime minister was the head of government.

Changes in Nepal's Political System:
In 2006, Nepal underwent significant political changes. The country witnessed a decade-long civil war between the government and Maoist rebels, which resulted in the deaths of thousands of people. In April 2006, a mass movement led by political parties and civil society groups forced King Gyanendra to hand over power to the people.

The political changes in Nepal led to the abolition of the monarchy and the establishment of a federal democratic republic. The country's first constituent assembly was elected in 2008, which drafted a new constitution. The new constitution was adopted in 2015, which established Nepal as a federal democratic republic with a president as the head of state and a prime minister as the head of government.

Conclusion:
Nepal's political system has undergone significant changes in the past few decades. The country was a constitutional monarchy until 2006, after which it became a federal democratic republic. The changes were the result of a decade-long civil war and a mass movement led by political parties and civil society groups. Today, Nepal has a federal democratic republic with a president as the head of state and a prime minister as the head of government.