The following happened while playing a Risk computer game variant, that was not the same as the traditional board game. This variant used a map of Europe, not the Earth. On this map, there are over a hundred territories (I can't recall the exact number). Most games on this map last a long time, and 100-army attacks are not uncommon. This map of Eurpope has continent-like areas, ranging from a huge one in Russia, to something as tiny as Portugal. The basic rules were the same as the "Classic" board game (except I used the setting where the numer of armies you get for turning in cards is the same for all turns, and does not escalate over time).
I found myself in a situation where it was just me and another player (played by the computer, with the "easy" AI setting). I controlled North Africa, Iberia, Italy, the Balkans, and the Middle East (except Turkey). My opponent controlled everthing to the North, and held a significant majority of territories and "continents". We both had thick walls of armies in a broad line, and my opponent was on the march, only recently having devoured all of northern Europe. He was coming at me hard and I was retreating. I thought it was all over.
Yet then I tried this strategy, straight from WWII. I concentrated my forces at one spot, punched through the enemy line (suffered 70% casualties), and galloped into his rear. I planted myself smack-dab in the middle of one of his "continents" with my remnant (which was still much larger than anything around it since he was concentrated toward his front as he pressed me). Hence, next round, my enemy's army allotment dropped sharply. He then proceeded to contain my encroachment, , yet I built it up so much that he did not waste armies attacking it. Instead, he pressed on against my front. The whole time, my enemy was now short one "continent".
So I tried the same thing a few turns later, on another "continent". Yet this time I used my new acqusition far behind enemy lines as a springboard to charge across the field and set up shop in the middle of another "continent." Sort of like an airborne invasion! I did this several more times over the next dozen or so moves until my enemy no longer controlled any "continents" and I still controlled a few. Granted, my enemy managed to push my line back a bit, and made some scary forays behind my lines, but he also siphoned off forces to observe my lodgements in his "continents". I made sure they were the strongest points on the board, to deter attack, building them up constantly, weakening my line to do so, yet never attacking from the lodgements. He attacked some of them and wiped out a few, yet I still managed to hold onto most of them.
Finally, I was able to hold off his frontal assault, and go on a slow steamrolling frontal offensive of my own. My enemy never recovered from this, and slowly I pulled up to each lodgement. When I did so, it became the strongest point of my line, allowing me to divert forces to each side to bolster the rest of my line. Eventually I pulled up to every lodgement and I won the day. I even was able to use some lodgements as springboards to swallow up one or two "continents," despite being so far away from my main advance. It was not a "bridge too far" as I had feared it might become. Yet if my enemy had stopped his frontal attack to attend to my "airborne" encroachments better than he did, perhaps he would have recovered.
I was amazed how I was able to come from behind by making concentrated attacks designed to frustrate the enemy's domination of his "continents". In some cases, the enemy might control 90% or more of the "continent", but all I needed was a strong presence in ONE territory, and to hold onto them "until the cavalry arrived". Never was so much won by holding on to so few territories.
It was Blitzkreig at its best!