I don't know, all Dumbledore/Voldemort has to do is have some method of escape when they get tired.

The main problem with this idea is that wizarding wars cannot be fought in a manner similar to any that muggle wars have been fought in. It would be different if wizards couldn't apperate, but they can. I'm not saying that is isn't possible to right this fic, but you're going to have to create entirely new military tactics.

Also, the differance between a competant wizard and the vast majority is staggering. I just don't see a competant wizard having much trouble destroying large numbers of average wizards and then running away.

A little bit a Fiendfrye goes a long way...

 

I think you are exaggerating. I don't think Dumbledore can beat 100 trained aurors, together in a open space. He most defiantly can take them one by one, but all at the same time is doubtful.

To negate the apparition issue, you make it so that there are only a few apparition points in the whole country. There would obviously be a few aurors at each post, strategically placed. You will be able to overpower the gaurds, but a great cost/risk, and it will alert the rest of the aurors.

Brooms/magical carpets will be used for hit & run operations while on the broom/carpet or to simply cross the border. Dumbledore will most probably use muggle means [undetectable planes... or even a freaking taxi will do the job], as the other forces won't be protected from it, for a while.

I would think of more when it's not 2 in the morning.

 

The problem I see with this argument is simply that the idea demands a well trained wizarding army, not a bunch of half-wits who barely scrapped by in Hogwarts. They might have been that before they were trained, but after training, they would be a force to be reckoned with. All of them can apparate, all of them are trained to "shoot" with thier wands to a fair degree, and if the leader-guy is willing to adopt anything of muggle psychological tactics, could train his army to be shooting killing curses without compunction.

Of course, this would force the allies to begin training up an army of their own.

 

Well the apperation and portkey issue isn't really that much of a problem. The GESTAPO controlled everything and spied on everyone in Nazi-Germany.
So get the same thing for wizarding GB. Anti-Portkey and Anti-Apperation-Wards, border patrols, listening devices. Everyone that apperates get's redirected to certain checkpoints in the next layer of wards, before he can be on his way again.

And why not get the muggles involved aswell? They would begin to question things for sure after some time , when the ministry has to worry about other things then obilivating witnesses of magic.
Although you would need to find ways to circumvent the use of nuclear weapons in my opinion (for example a mixture of an interceptor rocket and magic). They would simply be overkill against everything resembling a wizarding army.

Then there is the Fiendfrye spell again. Since Crabbe or Goyle can cast it, that says a lot about needing competent wizards in a wizarding army.

The problem I see is creating competent opponents for Dumbledore and Voldemort, if they fight on the same side. Freeing Grindelwald would be a possibility.

A good reason for the US joining would be the danger of a dollar breakdown for example. The Chinese are keeping the worth of their currency under it's real worth to push up their export ratio and they have a lot of US-treasuries and dollars themselves and as far as I understand it if they sell all that shit it would be bad for the Dollar (or something like that). Would be a good enough reason though.

The real problem I see with writing this story though is, that you would need a freaking amount of knowledge about modern warfare and weapons as well as. But if you have that and a decent writing style this story would be epic win.