Red Line-Fourth Reich War

The Red Line-Fourth Reich War is a major conflict fought between forces of the Red Line and the Fourth Reich.

The result of an ideological struggle, the war has caused widespread destabilisation and economic damage across the Metro. It's possibly the longest and bloodiest conflict to ever occur in the Metro Series.

Origin of the conflict
The war is believe to have originated from the Hansa- Red Line War, the first conventional major conflict fought in the Metro, between the Red Line, and an Anti-Communist Alliance composed of the Hanseatic League (Hansa) and the Arbat Confederation. Many believe that radical or dissatisfied members from the Coalition split off to form what became the Fourth Reich, in order to continue the war against the Red Line and eventually seek their destruction. The tension cannot be drawn back to a specific point, but since their formations, the Red Line and the Fourth Reich have always been hostile to each other.

Early fighting
Fighting was initially limited to numerous skirmishes and low-level violence until recent years where the Reich and the Red Line had been clashing severely, and the escalation of violence between the two can be considered the second conventional war in the post-war Metro. This soon turned into a total war, with each side using the majority of their resources in the conflict.

Battle for the Bridge
One major battle of the war is noted and actually experienced in Metro 2033, The Battle for the Bridge, which is featured on the level "Frontline". By 2033, the front line had become stuck in an endless stalemate with constant fighting over a large two tunnel-wide section located between the major Lubyanka and Tverskaya stations, controlled by the Red Line and Reich, respectively.

The battle has become infamous among Red and Nazi troops alike, who refer to it simply as "Bridge", for the extreme amounts of violence and casualties. The Red Line often launch wave attack upon wave attack of untrained and poorly equipped troops at the Reich's defensive line, but are always slaughtered by the superiorly trained and well equipped Reich army. As one Red soldier describes it "Attack, counter-attack, attack again no end in sight". Despite the Nazis suffering very few casualties, the relentless attacks have stopped the Reich's ability to mount their own assaults, repeating the cycle.

Ceasefire
By 2034, an unstable truce had been negotiated between the two factions. Although this halted most of the regular violence, their relations were still cold at best, with spies from both sides have been rumored to operate in each others territory and minor skirmishes are still numerous.

Red Line Offensive
After the Polis Peace Conference, the truce was broken when the Red Line launched a massive offensive against much of the Metro as part of their overall strategy to conquer it. Major combat between the two reignited as a second front opened up in the southern tunnel that connects the Red Line and the Reich. The offensive against the Nazi fortifications which included a combination of human wave attacks, heavy assault infantry, and a large armored tank rail-car, was repelled by Reich stormtroopers.

Aftermath
While the result of the offensive cannot be confirmed except that it was a failure, it can be assumed that it severely damaged the Red Line's fighting capabilities, as much of their best men and equipment were lost.

Reich Offensive
With Red Line being preoccupied with dry rot epidemic that decimated its mushroom crops, the Reich planned to take over the buffer station of Theatre (Teatralnaya) located between the two factions.

Though the Communists were taken by surprise, they quickly retaliated and after days of fighting took over the Armory (Kuznetsky bridge). From there they threatened the exposed Nazi station of Schiller (Pushkinskaya). Realizing this threat, the Nazis blew up the tunnel between the two stations which resulted in a catastrophical flood that destroyed the Reich.

Other factions
The war in recent times has caused major destabilization and affected trade through-out the Metro, especially in the central stations. Any settlements near even a small Red Line and Reich skirmish are vulnerable to being ransacked, and trade routes have suffered as the conflicts prolong. This has resulted in attempted intervention by Polis, while Hansa tightens its defence's near its borders with the two powers, however still retains trading relationships with both sides.

Casualties
Both sides have suffered large amounts of military casualties throughout the war, more so the Red Line than the Reich because of their frequent use of human wave attacks. But after the failed Nazi offensive against Theatre station and subsequent destruction of the Fourth Reich they sustained massive and most likely catastrophical casualties. However, in Metro Exodus, the flooding is never mentioned and conversations between Hansa guards indicate that the Reich's military is still combat effective.

Trivia

 * The Red Line-Fourth Reich War might be a reference to the Eastern Front in World War II, which was fought between the Soviet Union and Nazi Germany, from whom the Red Line and Fourth Reich are based off.
 * It's unknown if the war originally existed in the book before the game release. However, it can be assumed that since Metro 2035 will be a retelling of the events of Metro: Last Light, that the war is indeed canon in all Metro forms of media including the novel Metro 2033. It's still possible that war between the two was ongoing in the Metro however the reader never sees or hears of it. This is most likely because the Reich is only encountered briefly in the book and Artyom never sees the Red Line.