What decides an endgame with two soldiers against one, and no other pieces on the board?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws and is regression-tested against the official 110-diagram repetition casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it against the engine before publishing.
Direct answer
Whoever's soldiers are more advanced and better positioned to support each other, usually the side with two, tends to win the race. The extra soldier is not just extra material, it is an extra option: one soldier can shield or support the other's advance once it crosses the river, something the single-soldier side has no way to answer.
Why two soldiers usually beat one even without other material
A single soldier advancing alone can be blocked by the defending general covering its path; two soldiers advancing together mean the general can only physically block one file at a time, leaving the other free. This is the same coordination advantage covered generally in how multiple passed soldiers work together, reduced to its simplest possible case.
Counting the race correctly
Treat it as exactly the kind of race described in soldiers-only endgames: count how many moves each side's most advanced soldier needs, factoring in how much the defending general can realistically block given it can only cover one file at a time against two.
Related questions
Is this always winning for the side with two soldiers?
Usually, but not automatically; if the single soldier is much further advanced and the general cannot reach in time, the race can still favour the side with one.
Does file spacing between the two soldiers matter?
Yes, soldiers close enough to support each other's advance are considerably stronger than two racing on completely separate, unsupported files.
.