Multiple groups with grudges against the Nationalist formulated this plan together. They drew out Adam Preston and had him fight a tough battle where he sustained energy and used a decent amount of mana, then waited for the perfect opportunity to detonate the explosives that they lined the entire building with. The group that Adam Preston just killed was just a scapegoat. He was led to them by the group that was now attacking his headquarters.
That was the red light that the vice leader of the Nationalist saw causing him to tell the leader to leave. However, they did not know that they were being watched through hidden surveillance cameras.
The explosion had two functions. The first was to injure the leader of the Nationalist and the second was to draw him and the vice leader away from their headquarters. Those that were attacking the headquarters were all sorts of weaker groups and a few individuals that were unaffiliated, but they wanted in on the attack.
