If you are looking for something interesting like the Trojan Horse or crazy weapons/tactics then you must look no further than Greek Fire!

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

Id rather have the SAS storming in to rescue me form some terrorists, than the SEALS. Both are awesome, but I pick the SAS. Mind you the SBS are more comparable to the SEALS.

Well the Mongols are an easy choice.

But what did they actually conquer? Sure, they did manage to get the greatest (continuous) Empire the world has ever seen, but is was nearly all empty plains. Their expanse was still halted by the Germans of the Holy Roman Empire, so aren't they stronger? Conquering the steppes and oriental cultures was no problem, bu this means that the second the Mongols encountered a nation with advanced technologies, things didn't go so easy anymore.

Not dismissing the Mongol achievement of-course, I mean they did manage overthrow the mighty Chinese Empire at the time, but just to put that out there.

While being formidable warriors, all the Spartans did was lose. They just didn't do enough with their military knowledge to be nominated I think.

I think there are only three forces in history which realistically could be considered to be the "Best Military Force of all Time."
These three have all showed to overcome overwhelming odds, trekked through and conquered massive populated areas while encountering great resistance. Naturally, they were decisively victorious, if only for a time:

- Alexander the Great's Macedonian army against the Achaemenid (Persian) Empire.
- Napoleon Bonaparte's French army during the French Revolutionary Wars against the superior powers of Europe overthrowing all of them.
- The Allies invasion army during the final stage of WWII against Nazi Germany starting at D-Day in 1944.

Arguably, the Nazi German army at the start of the war could be included as they swept across Europe undisturbed, but they never achieved full victory. The second arguable nominee are the Romans, but they had only a very sound global strategy. There was not one single campaign which overcame all hardships. Thirdly, the armies of the Crusades might be considered. While they encountered great resistance, these armies never conquered any land beyond the immediate surroundings of the target city.

EDIT: I prefer to declare Alexander the Great the winner. Macedonia was tiny, when the Persian Empire was massive. Realistically he had zero chance to win, but did so anyway.

I'm going with the Mongols too, they conquered territory at a rate never before seen and forged an empire out of virtually nothing.

Easily mongols. Today there are only 10 million ethnic mongols (compare that to 1.3 billion chinese) so just imagine how few they were past then. Despite this they conquered and ruled lands that had over one hundred million people. Damn.

Hannibal and his elephants. He almost had it as well.

What? You ask about military force and I see battles in the poll? Then, I agree with S.Peelman, Alexander's army was something else, and his war machines were developed by Aristotle! The Battle of Gaugamela should be in the poll.

They weren't halted by the Germans, Templars nor Polish.  They withdrew from Europe due to in fighting mainly.

"As it developed, the Mongols did not remain long in Hungary, either. On December 11, 1241, Ogadei died in Asia. Upon learning of the great khan's death, Subotai reminded the three princes in his army of the law of succession as laid down by Genghis Khan: After the death of the ruler all offspring of the house of Genghis Khan, wherever they might be, must return to Mongolia to take part in the election of the new khakan. Recalling all their forces, the Mongols started back to their Mongolian capital of Karakorum, postponing their invasion of central Europe for another time–a time that would never come."

http://www.historynet.com/mongol-invasions-battle-of-liegnitz.htm

While even that link seems to draw a few things into question though.  A few people commented on some things not being completely accurate in the article.  However, there was no major Mongol defeat in Europe that I am aware of.  They simply left is what I understand.  I can't say that article is completely accurate but it does highlight some of their advance tactics. 

"Things were not as they seemed to the European knights, however; they had fallen victim to one of the oldest tricks in the Mongols' book–the feigned retreat. The riders of the steppes, unlike the knights, had been taught to retreat as a tactical move, and in so doing, they drew the knights away from their infantry. Once that was accomplished, the Mongols swept to either side of the knights, who had strung out and lost their own measure of order, and showered them with arrows. Other Mongols had lain in ambush, prepared to meet the knights as they fell into the trap. Whenever the Mongols found that the knights' armor afforded effective protection against their arrows, they simply shot their horses. The dismounted knights were then easy prey for the Mongol heavy cavalrymen, who ran them down with lance or saber with little danger to themselves. The Knights Templar made a determined stand, only to be killed to a man."

You asked what they destroyed or conquered?  How about China, Russia, Persia, etc..  While most of their land might have been "empty plains" they did conquer/destroy plenty of major cities.  If you can show me a major battle they lost in their European campaign then I'm all ears (Mongols cutting off ear of each victim pun?).  I just don't know of any and usually they even used retreat to their advantage.

Bold: Yes, yes, that happened. You are correct. It definitely had a part in it, but the Mongols just stopping at the borders of the Holy Roman Empire is no coincidence. They knew they were powerful as well and the Frankish kingdoms beyond also, and the Mongols didn't return afterwards. If that was because they didn't think they could win, or if they didn't feel like is was to be beneficiary to conquer Western Europe too, I don't know. Anyway, they never fought a formidable European army.

Italic: I give you China, as I already said. Russia however, was not yet noteworthy as power is concerned and Persia was over a thousand years past their prime. Sadly, I admit I don't know of any major battle they lost, besides those against me in Medieval Total War, as I also don't think there was any significant loss. I do think they weren't really tested, which is kind of the point.

All in all, I definitely recognize the Mongolian achievement as they did incite great fear across Europe, but overall with 90% (not actually 90, but just so-to-speak) of their conquered land offering very little resistance, I'd say they aren't the world's best military force. Especially when Alexander faced terrible odds as he was massively outnumbered and from a tiny kingdom compared to his adversary, odds which he overcame when he also didn't lose a major battle.

They weren't stopped by the Germans. They kicked the asses of the heavily armored (slow) European Knights. It was just that they thought Europe wasn't worth conquering (their grand invasion of Europe happened before they finished conquering the Mid-East or China, both regions that were doing much better culturally and economically at the time), for one, and 2 (which was the real weakness of the mongols) they didn't do well in high-humidity environments, which the further West you go in Europe, the wetter it gets. That's also what kept them out of South China for a long time (their final victory over the Song was more like a normal Chinese war than the rest of Mongol conquests).

Plus they had the best engineers of the conquered Jurched Chinese. They were not technologically backwards.