Complex sentence: Police from Merthyr Tydfil arrived soon after and took charge of the search-and-rescue operations; as news spread, hundreds of people drove to Aberfan to try to help, but their efforts were largely in vain.
Split into simpler sentences: Police from Merthyr Tydfil arrived soon after and took charge of the search-and-rescue operations. As news spread, hundreds of people drove to Aberfan to try to help, but their efforts were largely in vain.