The “Lallup Kaba” refers to:

Forced labor system
Religious pilgrimage
Cultural festival
Military expedition

The correct answer is: Forced labor system.

The Lallup Kaba was a system of forced labor in Bhutan that was abolished in 1959. Under the system, all able-bodied men were required to work for the government for a period of three months each year. The work could include anything from building roads to repairing bridges. The Lallup Kaba was a very unpopular system, and it was one of the main reasons for the Bhutanese Civil War.

The other options are incorrect. A religious pilgrimage is a journey to a holy place. A cultural festival is a celebration of a particular culture. A military expedition is a military campaign.