my best was the invasion of France in hww (i was usa)
I had shared map with him
He had a big army of medium tanks but they were all lvl 1
And idk why, but he placed all of his troops near Belgian Congo.
He was afk for a while and japan (his ally) told me to attack him before ai takes over
so i used his own airstrips to destroy his troops with rockets
for one whole day there was no opposition








but then i got afk and ai canada conquered me.

yeah.

Cool topic but I'm going to move this to general discussion. Q+A sub-forum is a topic for people that need questions about the game's mechanics, strategy/tactics or bugs.

Best invasion? Hmm, here is a recent, one-and-a-half day war I had, playing as South Africa against Germany in HWW, day 28-29 (Game end: day 30).

Some background information: About on day 10, Japan invaded Poland. At that time, Japan was the fastest-growing empire, obliterating any and all countries in his way. Germany, being an ally of Poland, attacked Japan. As South Africa, I was busy making my presence in the Middle East, conquering French West Africa and being allied to Britain. I had sensed Japan as a threat, so when Germany, struggling against Japan, asked my help, I gladly accepted. However, with a tiny army at the time, I needed time to prepare. Germany, still struggling, was starting to get impatient, and asked me to hurry on about day 12 or 13. Before this time, he had unilaterally gave me share map, but as I feared the German war machine bearing down on me, I gave share map back to prove I was actually preparing, and attacked Xinjiang, Japan's neighbor and weaker ally, who happened to also have interests in the Middle East. A day later, on day 14, I also attacked Japan.

Although my entry into the war was fighting a minor front, I managed to inflict heavy casualties on Xinjiang and Japan, destroying their navies with my own at little cost, and similarly, Germany also began to turn the tides. Fast forward to day 17, Japan had went inactive, and by that time I had dealt 112k casualties against him at the cost of 22k of my own, while Germany had dealt 64k at the cost of 52k of his own. Having defeated a larger share of the Japanese military, I expected a larger share of the pie that was Japan and Xinjiang. I was quite wrong.

Having allies doctrine meant that my armies were slower and took longer to conquer. Germany swiftly took many cities, although I took many provinces. It was from that time that I decided I would build up my forces against Germany and backstab him in the future. However, I needed a foothold in Europe.

Fast forward again to day 23. By this time Germany and I had conquered the UK, who had become inactive, and we became the only two active players left. Coincidentally, AI Spain attacked me, allowing me to take its African lands, yet as I prepared to take the Spanish core, Germany requested that I leave that to him instead, even though my spy revealed I had already obliterated much of the Spanish military. Quite angry, I told him I'll take it instead, and it was then Germany began to focus his forces against me, while his VP count inched closer to the solo victory count.

Fast forward again to day 27/28. Germany also attacked Spain, taking its relatively empty French lands. He also had built up a formidable fleet of almost purely battleships, and his total army size became more than two times of mine (600 ish units vs my 250 ish units). Although still having air superiority, I felt eventually Germany would outnumber me even in planes, as he already has in land and naval units. On day 28, a few hours before day change to day 29, I decided to attack, despite seeing four nuke bombers in Berlin, out of my aircraft bombardment range in Spain and south Italy (against Germany's wishes, I had established a foothold there earlier).

As luck would've had it, Germany was online when I attacked him, and he immediately staged a counterattack, pushing me back in the Caucasus, Central Asia, and China. I had a extremely inferior land army, which meant I could only win where I have an airforce, which was mostly focused in Europe at the time, fortunately. I completely obliterated every single German unit that came charging into Spain, pushing my limited units into France. That's when the nukes arrived.

A nuke targeting Algiers. One targeting Oran. One targeting Madrid. Except for Algiers, which was useless, the other two are vital airbases for my invasion of Germany. Accordingly, with the exception of Algiers, I protected those cities well, destroying the nuke bombers. When I took bordeaux, I built an airbase there, acting as forward base for my rapidly advancing troops.

That's when the last Germany nuke bomber bombed Bordeaux. Fortunately, a nearby airbase in Bilbao allowed my planes to not get grounded, but it was quite devastating. My armies were also stretched extremely thin across all fronts, having only a 9-unit airforce attacking a 16-unit stack with AA in China and 7-unit naval bomber attacking a 10-unit battleship fleet off Korea. I also completely gave up on the Caucasus, sending two armored cars instead to drive deep into German-occupied Russia and Poland (one survived the war and is in Warsaw). However, my West European and Italian front was pushing well, and I was determined not to lose that momentum.

Then, in the morning, as I was traveling to school, I saw Germany's feared 56-unit doomstack, originally stationed in Prague, its capital. It was his largest single army to offer and had a whopping 2.6k health in total. With the exception of a 10-unit interceptor and 8-unit tac bomber force, I sent my entire European airforce against it, even though it had a large number of AA. A few hours later, after school, I checked the game again... and it had been defeated in Mendes, France. The doomstack never reached Spain. With the last major piece of resistance gone, France and West Germany was basically mine to take.

East Asia also began to fare well. I was able to spare some air units from Europe to China, and I defeated much of the armies there, pushing north and east into Manchukuo and Korea. The sole German navy there, the 10-unit battleship stack, had been destroyed.

As day 29 drew to a close, I had conquered Cologne, Munich, and Stuttgart, pushing into Erfurt on the European front, conquered Warsaw with a single armored car, and had conquered Heijo and Fusan in Korea. Finally, on the eve of day 30, I won, grabbing a total of 1740 VPs compared to 1360 on day 29.

Casualties:
South Africa - 166,465
Germany - 590,912

Germany had lost an approximate 300 units in one-and-a-half days, while I probably lost around 60-80. Before the war, he had around 650 ish units, while I had 300 ish. On day 30, with the reveal of everyone's armies, his unit count is: 340, while mine is: 328.There was still much chaos despite defeating most of his armies there. Lyon, Marseille, Bordeaux, and Paris had rebelled. Despite having only minimal ground troops, the overwhelming air superiority won me the war.

Not a complete cleanup, but it's pretty much over on East Asia.

TL;DR - in the span of a day and a half, I had dealt >500k casualties to Germany while suffering >150k, winning the game by day 30.

Extra note: at the beginning of day 28, Germany possessed 40% of the world's military strength, while I possessed 31% due to my more advanced but far smaller military.