After testing out, I find that there are several gamey tactics to do as close a world conquest as possible, playing either as France, Germany, or UK in AHD. Of the 3, Germany stands the best chance.
1. They have Ruhr boom (no pop decline)
2. Great Germany saves you a lot of hassle, since it consists of numerous small states
3. Its location at center Europe solves the logistical problem of invading Russia.
4. They have jingoism & pro-military conservative parties.
The tactics are:
1. Research steamer tech as your first tech. Grab Zulu and Tunisia early while warring Austria for power projection.
2. Grab strategically located French's Africa and West Indies colonies early.
3. War England and Russia simultaneously early, after done dealing with France and Australia.
4. Always target GPs with multiple allied spherings.
5. Do humi + conquest war combination.
All these, I can manage (see screenshots), but I can't manage rebel. By 1900 or so, I have 1.75G pop, 4,500 brigades of standing army, highly concentrated in strategically important location. But 2000-3000 rebels pop up every 2 years or so ALL OVER THE WORLD. It is really frustrating...
Before you ask, I have done everything to minimize militant, but with constant warfare, it will goes up regardless...