1. The Dominion
Weyoun ruling the world with the Neverland Ranch as seat of power

. Freedom of speech abolished. Dissidents desintegrated. Jem' Hadar troups everywhere. Changelings replacing the Federation president and his/her staff.... Starfleet is destroyed, its ships and resources confiscated. Promising people are cloned, loyality included into their genetical profile. Weyoun recruits the help of a certain Crell Moset........ Horror, I fear.
2. The Romulans
Taking their hands on every federation technology to secure their supremacy. Tal Shiar presence everywhere: Paris, Berlin, New York.
3. The Klingons simply take the resources they want. They have to fight uprisings, but they will prevail. Enslavement follows. Sick, frail and old people were dealt with... There is no need for the Klingons to keep them alive. They don't contribute to their wealth, they just squander resources.
Dark prospects, indeed.