Honestly this entire situation with the academy, foreign nations, and the church of slaughter doesn't make sense. The sheer amount of attackers showing up is nonsensical. The church of slaughter is basically a spy/assassin organization and foreign nations don't have 100% of their citizens willing to launch suicidal attacks for very little reason. Having a number of elites placed strategically and launching towards several objectives makes sense, whereas this outnumbered situation doesn't work. Besides all that, both the church of slaughter's and the foreign nations motivations in this case are rather suspect. The church apparently wants the princess, which is small scale and few operatives are more appropriate rather than revealing the affiliation of hundreds of members. The foreign nations (I assume) want to kill Bloed and destroy academy city in general. They have very little reason to cooperate.