Why was France so successful in fighting against powerful countries in the late 18th century?

From 1792 to 1802, revolutionary France fought a series of
wars with other European powers.  By the end of that time period, it had achieved
territorial gains that the kings of France had wanted for centuries but had not
achieved.  There are at least two major reasons for
this:

First, there is the fact that the French armies were
quite large and quite well motivated.  The French were, for the first time, fighting for
their own country as opposed to fighting for the dynastic ambitions of their kings.  The
French Revolution is credited with creating nationalism as a major emotional and
political force.  By creating and playing on nationalism, the Revolution was able to put
larger and more motivated armies in the field than the autocracies that were fighting
France.

Second, there is the importance of military
leadership.  Though Napoleon was not yet emperor, it was during these wars that he
became the leader of France's military and eventually of France.  Some amount of credit
must be given to Napoleon's military abilities.

We can say,
then, that this French success was due to the size and motivation of its armies and to
the quality of its military leadership.