During Operation Barbossa, the codename for Nazi Germany’s invasion of The Soviet Union, one of the main hindrances to the invading force was the larger gauge of train track used by the Ruskies. Like Great Britain and America, the majority of Russia’s interior railways were 5ft apart. In the very first Russian railway the gauge was 6 feet, and back in 1841, an American railroad consultant and a Soviet Minister both pitched differing gauges to the Tsar. By Imperial Decree, the Russian gauge was set at 1524mm. The majority of Europe proper was using a 4ft 8-1/2 gauge.
Deciding between 4ft 8-1/2″, 5ft a.k.a 1524mm later shortened to 1520mm, or 6ft sounds very intimidating, and since it involves large pieces of machinery travelling at high rates of speed probably more academic than it is. In reality, the differing of gauges boiled down to personal preference and economic feasibility. As railroads grew, many countries found uniformity within their own borders to be cost effective, but they didn’t necessarily worry about uniformity with their neighbors. No use spending extra money to get to 5′ gauge when you already had 4ft 8-1/2″ in half your country.
And just like that a decision made 100 years prior to the invasion of the Soviet Union, helped decide the outcome of the war. The Nazi invaders were forced to send their engineering teams out ahead of their supply lines to lay down the gauge required, which exposed their men to enemy fire. The bridges and infrastructure of the Soviet Union also weren’t build quite sturdy enough to support the heavier German trains loaded down with supplies and would often creak and crash on their own.
The Germans typical blitzkrieg invasion was slowed to a crawl by multiple circumstances, and their inability to travel farther than they could supply their lines. The Nazis quickly found themselves in a deadly war of attrition, and as they were forced to withdraw in 1944, they did their best to trash the place on the way out. Using a “Schwellenpflug” to destroy the converted rail lines behind them as they went.