I think they were in fact hoping for political pressure - of the international kind. As I recall, the rebels had envoys in England and France who were trying to get those countries to pressure the US to let the south secede. But that task would be much harder if the rebels were conducting a guerilla insurrection, as opposed to trying to set up a government and army. Appealing to foreign powers not that crazy of an idea; a large part of how the US gained independence was that the French were persuaded to intervene on our behalf.