Contribution of martyrs are very important for nation building
Answers
I think we need to define nation building here. In terms of establishing a nation state, i.e., a country where the population primarily sees itself as being off that state, then it probably is not that important.
If on the other hand, one is looking to define a people as a nation, distinct from their neighbors, then the importance of Martyrs probably cannot be overstated. At this point we are no longer talking about simple nation building, but the establishment of nationalism, which in many respects resembles and indeed often competes with religion. Martyrs essentially tap into the romantic sense that we all have where we want to be part of something bigger than ourselves. By choosing to die for a cause (either explicitly, or implicitly by agreeing to fight for said cause), they validate the worthiness of the cause they have died for. It is one thing to say that one people should be distinct from others. Its another entirely to die for it. To look at the example I am most familiar with. In 1916, the leaders of the Easter Rising were executed after their failed rebellion. They failed in part because most of the Irish at the time did not believe in their cause. Their deaths however played a major role in the Irish recovering their sense of a distinct identity as not merely being part of the United Kingdom, but of belonging first and foremost to Ireland… an Ireland that should be free.