Tucker and his associate bully the foreign minister into altering Liza Weld’s position paper so drastically that it winds up being for an invasion rather than clearly against. They then use this document as the “smoking gun” intelligence to convince members of the UN Security Council to endorse war (with an unnamed country that is clearly Iraq).
Foster has toyed with the idea of resigning in protest but because he waited until the vote, Tucker has him fired before he can resign. Karen Clarke does resign in protest, but Lt. Gen. Miller (Gandolfini) at the last minute backs out of their agreement to both resign.
The last scenes show Liza Weld joining the staff of hawk (and previous enemy) Linton Barwick, Judy Molloy greeting her new boss, and Toby Wright (who leaked the position paper to begin with) leaving his desk, presumably after being sacked.
Thanks Jon S!