The bombings were the (very real) casus belli for USA's war with Al - Qaeda. (politics.stackexchange.com)
My question is basically, Does refusal to let Country A supply their troops by Country B constitute a legally valid casus belli as per international laws and norms? (politics.stackexchange.com)
IOW: casus belli just means you have a justification that most will consider sufficient something other than a minor disagreement. (politics.stackexchange.com)