Babylon 5, Season 4: No Surrender, No Retreat

[last lines:
Sheridan and Ivanova have viewed video of Earthforce ships destroying civilian transports carrying refugees from rebel planets]

John Sheridan:
This madness has gone on long enough. I don't care if we're not ready. I don't care if we're outnumbered and outgunned. I don't care what ISN says about us. This stops, and it stops now! Now if Earth wants to declare war on us, then it is time we took that war to Clark. You tell the others. Starting right now, we fight back and we fight back hard!

Susan Ivanova:
I thought you were looking for some other way than firing at our own ships. They were following orders.

Sheridan:
Any crew that executes an order like that is guilty of war crimes, and they deserve whatever they get. No, we're riding in, Susan. Anybody who wants to defect and join us? Fine. If they get in our way, we will knock them down. If they kill one of our ships, we'll kill three of theirs. And we keep going. We never slow down, and we won't stop. We're going after the colonies, then Mars, then Earth…and God help anybody who gets in our way.