Conversation so far:
When did Patrice Lumumba's deposition of Kasa-Vabu happen?
5 September 1960, Kasa-Vubu announced the dismissal of Lumumba. Patrice Lumumba heard of the firing and made three broadcasts, defending his government and declaring Kasa-Vubu to be deposed

Question: What was the joint session about?
Self-contained rewrite: What was the joint session in which Patrice Lumumba was in about?