The closest thing in history is Julius Caesars conquest of Gaul (France). Caesars Armies were greatly(overwhelmingly) outnumbered but still won.
An Army of 700,000 is not going to subdue a united population of 300,000,000.
Since roughly half of that 300M is on the "other side," and a very large percentage, possibly a majority, of those "on our side" will go along to get along, the force comparison changes pretty dramatically.
Not even close.
The conquistadors of Mexico and Peru were outnumbered to a much greater extent than JC ever was.
Admittedly, their conquests were facilitated greatly by native rivalries, epidemic disease and resultant social collapse. But we're still talking utterly ridiculous disproportions in manpower.
The British conquered India with forces much less than a ratio of 700,000 to 300M.