What leads the Elven king to imprison the dwarfs?

Answer 1

The Elves felt they were being attacked and responded in kind. Since Thorin refused to tell them why he was in their realm, for fear they would want some of the treasure (he coveted the Arkenstone and feared others would try to take it), they decided to imprison him just to be safe. The Elves distrusted the Dwarves, and they had, for many years, been seen as beggars.

Answer 2

In The Hobbit the thirteen dwarves are imprisioned by the Wood Elves of Mirkwood because

1. Dwarves and Elves have never been on good terms, consiquently the Elves are suspisious that the dwarves were plotting some foul plan.
2. The Elves were very ticked that the dwarves kept interupting their festivites in Mirkwood.

When the dwarves are questioned about what they are doing in Mirkwood, they refuse to answer, making Thranduil (the Elvenking of Mirkwood) extremely suspious. As a result, the dwarves were to remain in prision until they revealed their intentions.

It should be noted that the dwarves were not badly treated while they were captives.

Answer 3

The Elven King captures them and puts them in his dungeons. They had strayed off the path in Mirkwood looking for food and were too weak to consider fighting. The Elven King accuses them of attacking his subjects, trespassing and being spies.