Kane's casual disposal of The Starscream. Up until this point you've been taking orders from Seth, a shady guy with a tendency to send you into missions with faulty intelligence (such as calling an area undefended when it is in fact heavily defended) and slight hints of envy towards you. He's also made it clear that if you fail, you die. He plans to send you on a mission that involves a frontal assault on the Pentagon itself. Then Kane is introduced for the first time in the game, by killing Seth.
Seth: You see, power shifts quickly in the Brotherhood. Kane has been loathe to attack America, but I think now is the time, and you are the one to do it. This is the Pentagon. A full-scale attack with your strongest forces should render their military center of oper-*gunshot*
Kane: Yes. Power shifts more quickly than some people think.
"Well. What shall we talk about, hm? Your powerful GDI forces have been emasculated, and you yourself are a killer of children! Of course, it's not true, but the world only believes what the media tells them to believe... and I tell the media what to believe; it's really quite simple. But now that I know where you live, Commander, it's only a matter of time. Were I in your shoes, I would spend my last earthly hours... enjoying the world! Of course, if you wish, you can spend them fighting for a lost cause. But you know that you've lost."