International Law: FHS-style practice paper

"The prohibition on the use of force in Art 2(4) UN Charter is rendered meaningless by the breadth of exceptions claimed by states, particularly pre-emptive self-defence and humanitarian intervention." Discuss.

State X is providing weapons, training, and financial support to rebel groups in neighbouring State Y. The rebels launch attacks on State Y's military installations from bases in State X. State Y's government requests that State X cease its support. State X refuses. State Y is considering using force against the rebel bases in State X. Advise State Y on the legality of such action under international law.