Most Notorious Military Blunders

[Kralizec]

In WW1 when the Ottomans entered the war they tried to attack Russia via the Caucasus while the Russians had their hands tied against the Germans and Austro-Hungarians. They had a decent numerical advantage at the start, too. I do not remember the details; but at some point the Ottomans had to retreat suddenly and the harsh weather conditions (winter in a mountainous region) killed a large number of men through frostbite and starvation.

[Arjos]

Maybe it's only me, but I never saw the invasion of Russia as a blunder: marching all those men, in itself was already an achievement, that required quite some planning.
The intended goal was actually obtained: getting to Moscow. Napoleon simply never considered that Alexander wouldn't surrender and probably thought the russian army wasn't disciplined enough to adopt a scorched earth tactic on that scale.

[ReluctantSamurai]

Speaking of the Nazi invasion of the Soviet Union in 1941...I've never seen that as a mistake. The Soviets were in the midst of a massive rebuilding program and at the same time were very weak in leadership due to the Stalin purges of the '30's. If a more consistent and less ambitious plan had been followed, the Soviets would've been in more serious trouble than they were historically. But....

.....let's look at the flip-side of that conflict. Despite the obvious German build-up, and advance warning from numerous sources, Stalin refused to believe that Hitler would attack. The result was one of the major military blunders in history.

[CountArach]

Maybe it's only me, but I never saw the invasion of Russia as a blunder: marching all those men, in itself was already an achievement, that required quite some planning.

The mere fact that supply and general logistics were that difficult implies that the entire project was probably too difficult to be realistically pulled off. Yes, he achieved his goal, but when the peace negotiations didn't go as expected he had no contingency plan. That's what made it so terrible in the end.

Not to mention the fact that Russia was actually probably a better friend than most of the other European countries at the time and as such from a grand strategic point of view (no personal grudges between the two rulers from memory and certainly note the same history of interminable warfare as someone like Austria or Prussia), it was just a daft move altogether.

[Arjos]

Even if he wanted to win the war with a single battle and reaching Moscow, similar to the campaign of 1805, he surely must've planned to winter camp there. So the contingency plan, could've easily been to march on St. Petersburg or something, coming spring.
Who could've foreseen the Fire of Moscow? In my view, it wasn't much of military errors on the french part, but a resolute defense by the Russians, throughout the campaign.

That politically didn't make much sense in the first place, I completely agree...

[LeftEyeNine]

In WW1 when the Ottomans entered the war they tried to attack Russia via the Caucasus while the Russians had their hands tied against the Germans and Austro-Hungarians. They had a decent numerical advantage at the start, too. I do not remember the details; but at some point the Ottomans had to retreat suddenly and the harsh weather conditions (winter in a mountainous region) killed a large number of men through frostbite and starvation.

Speaking of this ?

http://en.wikipedia.org/wiki/Battle_of_Sarikamish

[Kralizec]

Speaking of this ?

http://en.wikipedia.org/wiki/Battle_of_Sarikamish

I think that's the one, yes.