Gate: Thus, the Kovenant Empire fought there.

Act 4 part 2

Panic swept through the Saderan capital like a plague, and hysteria ran through the city streets, spreading among the countless conscripts who heard what the Kovenant was capable of doing, of how their weapons could destroy Saderan field armies in mere moments, stories of veteran legions being swept aside by an unstoppable force and how they wished to take this place as another one of their conquests. There are some exaggerations, yes, but right here and right now, what was real and what wasn't went out the window, as dread gripped the Saderan soldiers on the walls, peering out to see a truly massive Kovenant force on their doorstep, tens of thousands of Kovenant soldiers with their associated equipment and machines.

Such a force would have been easy to take care of, the Saderan capital can raise many times more troops and recall any of their nearby Legions. But this was different, even if the entire city was to mobilize, the commanders knew for certain they would be destroyed, and with water supplies and food limited, a prolonged siege would be all but impossible, Kovenant troops could simply cut the aqueducts and Kovenant artillery alone can demolish the city.

Yet, the Kovenant didn't, instead they just stood there, waiting.

"Why aren't they moving?!" A Saderan soldier exclaimed, gripping his spear tighter.

"I... I don't know... Wait, look! Those troops are moving and they have something!"

The Saderan troops watched as the Kovenant brought up droves of soldiers, all carrying strange metal devices on their backs and carrying a great many boxes. Quickly they began to assemble these devices and soon three dozen of them started loading strange oval objects inside of them and then, a sound came.
A series of heavy thumps.

Within seconds, explosions were heard inside the Saderan city, explosions on each of the highest buildings of the Saderan capital, yet, much to the surprise of the garrison, the buildings were not damaged, nor were the streets that the shells hit.
But the panic and fear were real, the few people who remained on the streets ran for their lives or hid in the houses that were open to them. Many of them fled deeper into the Imperial cities even as more shells hit and the sound of explosions could be heard miles away.

These were not standard mortar shells, these were specialized shells, designed to create massive explosions, loud and attention-grabbing, but these were never designed to harm or destroy, they were designed simply to break morale, especially among less experienced enemy soldiers. By firing these shells into the Saderan capital, the Kovenant was sending a message.
At any moment, they could very well take this place with little cost to themselves.

.

Emperor Molt paced back and forth in one of his office rooms, trying to come up with a way to confront the senators in the room beyond the doors. In truth there was very little he could do, his armies shattered, the finances were all but spent and now the Senate was out there, hounding him like a pack of angry dogs. Suddenly, a single legionary ran towards him.
"My emperor, the runners have just returned from the other vassal states... King Duran's domain, as well as all the others, will not be coming to our aid, they've abandoned the cause and have gone to fix public order issues in their own lands."

Molt's anger grew more and more, he grabbed the man by the collar.
"Then tell whatever forces are loyal to rush back here! Give them rewards, anything!"

"My lord we've already tried that and very few answered the call and what few forces that were able to receive the message weren't able to break through the Kovenant lines... The Capital is cut off."

Molt couldn't believe what he was hearing, a mere few months ago the Empire looked as though it was indomitable, unstoppable, and ever-lasting, but now it seemed that the pillars of gold that propped up the Saderan Empire were transformed, corrupted, turning into pillars of iron and rust and even those were starting to unravel, the hounding of the senate got louder and louder, he would have to face them soon.
But what else could be done? The Saderan army had been decimated, her subjects turned their backs to forge their own fates, finally free from the oversight of Sadera.