Alliances are most commonly regarded as a response to an external threat. The level of threat is a function of relative power, geographic proximity, offensive capabilities and perceived intentions; other things being equal, an increase in any of these factors will raise the level of threat that a state poses to other. States usually join forces in order to balance against the greatest threats they face, although revisionist states and especially weak states will sometimes 'band-wagon' by allying with a strong or aggressive power.