Russia is returning two of its armored trains to active service. Russia made extensive (and widely publicized) the use of armored trains during its civil war in the early 1920s. Armored trains had been used before that, but not with the ingenuity, and on the scale, that the Russians demonstrated. The trains saw service again during the early 1970s, when there was a low level border war with China. When the Cold War ended, the armored training again showed up in the Caucasus. There, local separatists were attacking trains and blowing up rail lines.
It's not just the armor on the engines and cars that matter, but what the train carries. The current armored trains have anti-aircraft weapons (for use against ground targets), elaborate communications and electronic warfare equipment, railway repair troops and flatcars carrying tanks and other armored vehicles. The basic idea is that the armored train is basically a moving anti-terrorist unit. If terrorists are encountered, the armored vehicles are unloaded and go after them. Some of the new UAVs Russia is buying from Israel may end up on an armored train, providing air reconnaissance.
Russia has had railroad troops for 150 years. This paramilitary force was mainly there to provide security and emergency repairs. In most other countries, these services are provided by civilians. But Russia have always considered the railroads as a critical strategic asset, and the paramilitary were there to make sure the railways were protected, well maintained, and quickly repaired if damaged. There are currently 100,000 Russian railway troops, and a formidable opponent for any terrorist groups trying to cripple the railways. The railway troops have kept the armored train concept alive, as well as the ability to build and employ them.