The phrase "army behind" is correct and usable in written English.
It can be used in contexts where one is referring to support or backup from a group, often in a metaphorical sense.
Example: "With the army behind him, the leader felt confident in his decision to move forward with the plan."
Alternatives: "supporting force" or "backing group".
In August 1914, as a colonel and chief staff officer of the German 8th Army, he tried to persuade the 8th Army's commanding officer, General Max von Prittwitz, not to withdraw the army behind the Vistula River and so abandon East Prussia to the Russian forces.
Eugenie Bouchard 1 Li Na 0. First set was won by Li Na 6-2 Li Na to serve, now, the People's Republic of China army behind her, a force which numbers a thousand million billion, something like it, a lot anyway, versus Bouchard's "Genie Army" which numbers a dozen dudes without girlfriends in white T-shirts, my they annoy me, could be getting old.
Napoleon abruptly departed for France, leaving his bedraggled army behind.
Even Louis XVI had an army behind him.
Does he really have the Army behind him?
"You can't go to war without an army behind you.
Asad with the main Muslim army remained behind, but at the arrival of the Turgesh host, Asad's troops broke into a headlong flight for the Oxus, which they managed to reach just ahead of the Turgesh.
This army of behind-the-scenes programmers will largely determine who the big software winners will be in this, the Internet era of computing.
Efforts to integrate into a national professional army the dozens of private armies behind the warlords are underfunded and limited in scale.
There were also many Soviet troops still available in reserve armies behind the front.
They also massed a group of armies behind the front positions which they intended to use to launch their own offensive as a counterattack once the German strength had dissipated.
