Invasion: Finland (World War 3)

The Invasion of Finland was the last invasion by the CSTO in the western front during World War 3, and was the biggest victory for NATO, as it not only shocked the CSTO as they outnumbered Finnish forces 10:1, but handed the CSTO major losses, including many of its best snipers. The battle lasted nearly a year with heavy losses on the CSTO side, making the loss even more gut-wrenching for the side, it was deemed the worst plan since Operation Barbarossa in World War2

Prelude to the Invasion
Finnish-CSTO relations during the war slowly deteriorated, and the Finnish government nearly considered joining the war after the Battle of Berlin, but opted out. Finnish support was aimed at NATO and the Pacific collation during the Invasion of China is was gave the incentive to attack the nation since it was neutral, so it would be unexpected, and had a really weak military.

After the Battle of Warsaw, where CSTO forces retreated on purpose as a distraction for the plan, which actually worked until the day before the invasion, which gave the Finnish military knowing where the CSTO will be heading from and counter those areas.

Invasion begins
On August 23rd, CSTO rolled into Finland similar to the Winter War in WW2 and was already met with issues since the Finnish knew of the invasion due to undercover scouts and prepared for the attack. This knowledge caught the CSTO off guard and with NATO help, stopped the advance dead, but a stalemate formed and was brutal.

The main advantage the Finnish had was the sniper nests stationed around the Finnish-Russian border, which covered most of the border and were stationed in mountains and trees, making them impossible to find without wasting time and resources. These tactics was what prevented Finland from falling to the CSTO in the initial invasion.

CSTO invasion of Aland
Aland, a small island that was apart of Sweden, was a major area for the Finnish Navy, and was covered by NATO forces to prevent the island from falling into the CSTO's hands, but a naval invasion by CSTO members Belarus and Armenia from Lithuania, along with Russian help, invaded the small island and managed to take it, placing naval ships and artillery to attack major Finnish cities like Helsinki, which led to major civilian casualties, but few military casualties.

But on October 15th, NATO invaded Aland and began to take back the island, which led to the destruction of the Armenian navy, which made Armenia useless for the rest of the war. Despite the island being very small, the battle of Aland lasted 2 months and on December 6th, NATO forces finally took the island and the CSTO fell back.

CSTO advance of the Finnish mainland
With the defeat in Aland, the CSTO attempted to continue their invasion, which had been stopped only 15 miles from the Russian-Finnish border, and began to send troops through Sweden, which led to Sweden, a neutral nation secretly sending forces to aid Finland, to declare war.