Just before the siege on the last safe city, Gary gave a rousing speech to the soldiers under his command.
[spoiler]"Whether we wanted it or not, we've stepped into a war with the Vanguard on Earth, so let's get to taking out their command, one by one. Zavala, Ikora, and Cayde. From what I can gather, they command the Guardians from a Tower just outside of The Last City. With the right team, we can punch through those defences, take those vendors out and break their grip on the Traveler.[/spoiler]