The Resource Wars
The Resource Wars saw a change in the way war was fought. Fast moving predominantly air wars with space superiority were becoming unfeasible with constricting fuel supplies, economic downturns, and anti-war sentiments at home. With fewer jets and tanks, more of the fighting was being given to the army and marines. War was regressing to lines of artillery and infantry battles pitched across no-man's land. To better face this problem several first world nations engaged in a standard template construction system that would allow them to quickly and efficiently fortify and supply their lines of battle.
The uniform construction patterns made the new structures quick and easy to manufacture, and then move into place. These structures replaced trenches and barb wire as the main method of stopping infantry assaults. After a while, the uniform nature of the forts built proved a weakness. After breaching one, the enemy would learn the basic lay out and weaknesses of all of the rest in a similar design family. Stuck in uniform construction, the first world nations lost many STC forts, at high cost to the enemy, but lost none the less. These forts would be rebuilt and remodeled by the intruders, and attempts to retake them would prove costly as attackers were not prepared for internal changes, or adaptions made by the intruders.
The solution presented was for the first world nations to build MORE STCs, and of greater variety. The designs had worked fine until they were compromised. The new designs would need to be more modular and more adaptable. This was approved and more were built, half as an effort to keep in the fight for the dwindling resources in Africa, central America, and other places, and half as an attempt to bolster flagging economies. The solution was terrible, as this allowed the insurgents and terrorist factions to gain access to the new designs, which they were better able to exploit. Despite the technological and firepower advantages of the first world nations, they were simply slow to respond and slower to adapt.
The Problem Worsens
As the Resource Wars drug on, larger problem began to emerge. Desertion and low morale became rampant on all sides. After decades of war, many just wanted to hide from it all. Even the most fervent of militaristic nations were tiring of war. Grandchildren were fighting in their grandfather's war, and it was just an endless procession of flag draped coffins coming back. Eventually the war dead stopped being brought home and were buried in soldier's cemeteries where they fought. After some horrific battles, electric dozers would just cover the trenches over, burying the soldiers with their guns in their dead hands.
War equipment became problematic as well. Food and ammunition were scarce, and so was fuel. There were many installations where soldiers were outnumbered by tanks, but the tanks didnt have any fuel or ammo. They were just decoration. The same applied to helicopters, fighter jets, and any other equipment that hadn't been modified or designed to run on batteries or solar panels. Some very large STCs would be abandoned just a few years after being completed, others would be completed, but the military would have left with, or even before the contractors finished.
Judgement Day
There isn't an assigned date to the period of Judgement Day, and it is likely that it actually covered a span of 3-5 years. During this time, terror and insurgencies flared in the wake of retreating first world militaries. Like the battle of Dunkirk, they left almost all of their gear behind in a mad rush to get to the ships that would take them home, to expected safety. The terrorist and insurgent factions would take up these weapons, with what supplies they had, and would unleash generations of pent up social hostility. Nukes were launched, dirty bombs were set off, chemical agents were dumped in water supplies, cities were hit with chemical and biological attacks. These were largely facilitated by the gear left behind by the first world nations.
The STCs left in their wake were occupied and became the strongholds of regional bandits and would be warlords who use them like castles to rule the wastelands and badlands of the Second Dark Age, complete down to using stolen uniforms and archaic weapons.
Basic STCs
The Cube - a geofront STC, Cubes were engineered from sections of ship hull. Most navy ships were built in pieces and then welded together at the dock. The cube took the modular design philosophy and used it. An entire base could be engineered in days, manufactured in weeks, and put in place over a long weekend. Drilling and ANFO explosives would create the hole, heavy lift helicopters would drop each section in place, and then they would be welded together while dozers and heavy construction equipment buried everything but the access bunkers and observation towers. The cubes themselves were uniform, with barracks/personal quarters units, medical units, rec and galley units, arsenal and training units, and even underground weapons units, usually concealing short range ballistic missiles or other artillery weapons. Cube bases were quickly built, stocked, buried, and an alarming number were forgotten.
The Standard Fort - again built from preconstructed warship pieces, the standard fort was the superstructure of a navy cruiser with a curtain wall around it. The STC did not have naval cannon turrets, but did have a number of 3 to 5 inch cannons for defensive purposes. These were scavenged from damaged warships that were not going to be repaired, or from ships that were not going to be finished. The forts were typically named after the ship they were scavenged from, and almost all have since been destroyed, or damaged to the point that they are no longer useful for anything other than drifters and wasteland outcastes.
The Standard Watchtower - salvaged from the superstructure of a destroyer or frigate, watchtowers were mini-forts, with anti-infantry barricades and anti-tank ditches and obstacles. They retained the single gun turret of the destroyer, and this was the main watchtower defense. From a high perch, the tower was used for local surveillance and population control.
The STC Today
STCs are still used on occasion, as they are still a cost efficient design, but nowhere near the scope of their use during the Resource Wars. The Atlantic Federation and other new first world powers eschews the use of large terrestrial bases in favor of their fleet of ships and support from pre-con tactical bases that are easily moved with said ships. The de-emphasis of large scale war in favor of elite infantry versus elite infantry, and almost gladiator style mecha combat has rendered the main use of many STCs obsolete. The Cosmic Era simply no longer fights with massive armies of infantry and scores of tanks and a great multitude of artillery and waves of aircraft.