Answer: there may be many. But you can group them in two categories: those that are determined by international law and those that aren’t and result of a spontanous, abusive, arbitrary, chaotic, irrational, anarchic impulse that is punished by international law. Which is to say: if you make a war that keeps itself inside of international law, you can’t be hold for ‘guilty’, and thus your nation is not supposed to pay compensations for such an act, and the acquisition of territory or good is considered as ‘legal’. If the war is not inside of a legal frame, you may not only loose all the acquisitions but pay heavy compensations for the damage caused. Territory and goods acquired in defense, are a legal acquisition inside of International Right regulations (Israel).
Legal wars are those that result from: invasion of territory were it through earth, sea or air by contrary army forces. Acts of spy work by an official (diplomatic corps or related). What is called ‘ingerencia’, which is to say, the fact of intervening inside of inner affairs, were they related to justice, economy or politics with the intentionality of favoring foreign interests, by officials (governement linked personalities). International law considers that all acts of a nation linked individual are to be answered of by the corresponding nation. Even if private spywork or interference in inner affairs is not considered an act of war, if discovered and the nation not taking the corresponding measures, it may lead to freezing of diplomatic relationships and to further acts leading to war.
Were international law to be considered seriously, it is obvious that ‘spy work’ done through satellites is an act of war.
It’s obvious that many things happen without it immediately leading to war. Usually, minor problems or happenings are solved through economic compensation and war left for cases where this is not obtained or the recurrence of those happenings does show obvious hostility towards oneself.
Seen from that point of view, no contemporary war has staid in a legal frame. From France’s invasion by Germany in 1870/1, first world war, second world war, war in Vietnam, war in Korea, war in Croatia, Kosovo and Bosnia are illegal. Germany was thus obliged to pay heavy compensations to France for 1870, first world war and second world war, while this has not been the case for Vietnam, Corea and Yugoslavia (foreign recognition of independence is an interference in inner affairs that justified a war of Yugoslavia against Germany and certainly not an agression of those to Yugoslavia.)
This state of things resulting of the cold war and the practical refusal of international right by some countries (among which the Vatican) in the Final Act agreements of Helsinki, 1975, which have though no binding validity, has led to a point were arbitrarily any nation may agress another without consequences, while vilest inventions are invented in order to justify those.
A serious exception to this state of fact may perhaps be considered the Irak war, which makes appear factors as relevant that are not considered in International law, which is the absolute disastruous inner situation of the country.