How to project power over distance?
I've always really liked Ursula K Le Guin's idea of FTL travel: that actual FTL travel is currently and will always be impossible, and that a trip from one star to the next will take decades (even going a significant fraction of lightspeed), but that the transmission of information instantly over that distance could hypothetically be possible.
In this case, how could a government project power? Government only has power currently because its subjects believe that it has power and that its laws are significant, and this belief fundamentally comes from a monopoly on violence (being by far the biggest and most powerful organization in a given area, by sheer violent force). But over such a great distance, how could a government project that violent power? Certainly ships can't fly quickly, so say a colony on a different planet declares its independence, how could that be realistically prevented by a government by using instant communication alone?
How could this be done by an authoritarian, or even totalitarian government? By intentionally building computer systems which can only effectively be operated via data connection to the central home system?
TLDR: Given the idea that instant information communication between planets could be not only possible, but relatively costless, but actual transportation of matter/energy would take decades and be mostly impractical, how could a centralized interstellar government continue to project control/authority?