So there are multiple paths to a solo, although some clear patterns arise.
Option 1: be England or Turkey, and walk across the main stalemate line early. England gets Tunis/Warsaw/Moscow or Turkey gets Spain/Marseilles/Munich. Keep it while you scoop up all the centers on your own side of the line, which the other powers cannot stop. Examples:
gameID=156348,
gameID=118381,
gameID=46844,
gameID=81978.
Option 2: be France, make sure England has a weak opening. Grab Tunis, then use naval superiority to take out England, outflank Germany and force Scandinavia. Example:
gameID=133722, although there must be more.
Option 3: be anyone, play a strong 2-player alliance that sweeps the board. Both of you cross your respective stalemate lines, then fight it out for the solo. Example:
gameID=112043.
Option 4: be anyone, start strong but not too strong. Another power becomes a solo threat, everyone rallies to defend against him, and in the aftermath you grab a solo too fast for the rest of the board to coordinate. Example:
gameID=161926Option 5: be Russia, get to a strong 12/13, then try to win by brute force. Example:
gameID=39970.