By repeatedly splitting an army, it is possible to create tiny armies of just one man each. Tiny armies are almost always made using cavalry, since cavalry is faster than infantry and the cost of one man of either type is too small to matter. Tiny armies are useless in combat, but they can perform many other actions that require an army.
Tiny armies are also sometimes called "Single man armies" or "Scout armies".
Creating Tiny Armies
To make a tiny army, you need at least 2000 infantry, plus a cavalry unit that is as small as possible. When an army has at least 2000 total men (of either kind), it may be split. Thus, you split the army, then recombine the infantry (along with a halved cavalry amount). The resulting army can once again be split. This process can be continued until the cavalry unit is split down to a single man. He may then be placed into a new army. The result is a cavalry army of one man.
In general, it saves on clicking to start with an infantry unit of at least 4000 men, where 8000 or even 16000 is even better. Having a larger infantry army means you can split the army multiple times before recombining it. Splitting is easy; recombining is tedious.
Uses of Tiny Armies
Tiny armies can perform the following tasks, all of which require a land unit without respect to its size:
- exploring terra incognita
- capturing trading posts and unfortified settlements
- looting controlled enemy provinces, including synchronized looting. Note that looting happens before attrition is computed, so that you can send a suicide scout army to a winter province and he'll get the loot just before he dies.
- looting provinces occupied by enemy armies, regardless of fortification. Again, looting before attrition, so a single man can loot against a huge stack that kills him via attrition. Requires retreat on the exact day battle begins.
- directing retreats of enemy armies
- forcing retreat of a stack of allied armies
- occupying controlled enemy provinces to kill population growth
- tweaking natives to get them to rise, then running away
- losing warscore in battle in order to be force converted, to lose a province, or to prevent peace in a war you're in which an AI is warleader of.
- defending isolated trade posts by directing the AI to other unfortified provinces. (The AI prefers to target undefended provinces to those with any defense.)
- controlling the path that AI armies will take to reach a destination (see below)
When the AI decides to move an army to a destination, it chooses a path of least enemy resistance. Provinces containing no enemy units are preferred to those containing enemy armies of any size. The number of provinces in the path is a less significant factor. Thus, the AI will prefer a path through ten empty provinces to a path of two provinces if the first province contains an enemy army, even a tiny army. This is great for beating up China in the early game. Start a siege in Lanzhou: the AI marches its army there to break the siege. Next, move tiny armies into all interior provinces between Lanzhou and Beijing. Then besiege Beijing. The AI will send its armies to Beijing along the long coastal route, across rivers and mountains, which takes over 8 months. The AI army often won't reach Beijing before the siege completes.
Note that unlike normal armies, tiny armies are largely immune to movement attrition. (They do take fractional attrition, but it takes 50 straight month-ends of movement -- over 4 years -- to accumulate enough attrition to actually eliminate one.) This makes it possible to do certain things with tiny armies that would not be cost-effective with substantial armies.
Hazards of Tiny Armies
Although tiny armies are largely immune to movement attrition, they are very vulnerable to attrition from overstacking. If a province is even slightly overstacked, you'll see your tiny army having "999" for its attrition rate. This means it will die unless it can get out before the month end.
Tiny armies alone in a province will give a cheap and easy morale boost to any enemy army, including rebels, which may attack there. For this reason, it's best to garrison tiny armies together in a province along with a real army.
As passengers, each tiny army takes up as much space as 1000 men.