An obvious source of alliance durability is the exercise of hegemonic power by
a strong alliance leader. Alliance leaders can discourage dissolution by bearing
a disproportionate share of the costs, by offering material inducements to make
alignment more attractive, or by threatening to punish disloyal regimes. Athens
exercised this sort of leadership during the Peloponnesian Wars, Great Britain
used similar tactics with its own clients during its imperial heyday, and both the
US and the USSR used a variety of instruments (including the threat or use of
force) to keep their own allies in line. In extreme cases - such as Iran 1953,
Hungary 1956 or Czechoslovakia 1968 - an alliance leader may overthrow a
defecting regime in order to keep it within the fold