Why did Krule try to kill Cannonball?
In X-Force (1st series) #14, Krule was sent by Gideon to kill Cable. That way the Externals could safely take Cannonball under their wing. Krule found the team as their base was detonated and believed that Cable died in the explosion. X-Force fought against S.H.I.E.L.D in their helicarrier and, as the team finished choosing their new base of operations, Krule arrived and tried to kill Cannonball, because he saw him as a threat to the other Externals, who stated earlier that they wanted Cannonball to join them.
