Final answer:
The Gate took control of other channels by issuing a decree preventing them from airing other content, forcing them to broadcast its own programs, and making them replay its aggressive messages.
Step-by-step explanation:
The action that the Gate took to control the other channels was to first issue a decree that forbade the channels from screening any announcements other than its own. Secondly, it enforced its broadcasts on these channels, and thirdly, the Gate made the other channels replay its messages, which had become increasingly aggressive and intense after an event referred to as the Disgraceful Events.
While some networks complied with these demands, others refused and chose to shut down their channels and offices instead. This scenario exemplifies the concept of gatekeeping in the media, where entities in control of media outlets have the power to shape and influence the public's exposure to information. This process can have significant implications for how a society views and understands events, as the gatekeeper may present a biased or limited perspective.