If you don't give a pretext to go to war, you are the bad guys by default.
No one wish to think they are evil.
Also war are expensives, you need to justify an increase in taxes.
If you increse taxes in order to go to war because you are bored, you may have internal resistance.
Therefore your country is weaker and you have increased chancesto be defeated or at least to suffer politically.
Then you need to get soldiers, it is harder to get civilians to rush under the flags in order to be the bad guys. You need inspiring reasons.
Finally, now you got the problem of democracy. People are more concerned about internal affairs. Imperialism is not a popular idea nowadays, so you have to bring "Democracy".
As you may know, the excuses need more and more propaganda nowadays. You need to prepare your internal opinions. Civil wars are never black and white. You need to label first the side you wish to win as "Freedom fighters" or "legal government elected by the people". And the other side as "terrorist" or "bloody dictatorship".
You have many such examples, Kosovo war, Lybia War, Syria War.
Moreover the majority of excuses are plainly lies.
Truth is not important when you wish to wage war.
Internal and external support are deemed way superior to it.
Some real reasons to the conflicts listed above :
1) Syria is a fucking ally of Russia. Syria may be some useful country in the Chinese Silky Way.
There are concerns that the Civil War has started with a bit of help from Uncle Sam.
Moreover NATO countries or NATO allies have directly supported Daesh (Turkey, Quatar, Saudi Arabia).
2) France was partly a proxy to start an american war. Lybia was close to Russia. And Lybia wished to overthrow an african currency which is controlled by Paris. This currency gives Paris a large influence inside her former colonies.
3) One of the more likely reason to attack Irak is to stop the sells of oils in Euro.
The dollar is the world money, because oil is still mostly traded in dollar.
If the dollar usage drop significantly, USA won't be able to spend that much on military.
4) Crimea was a russian territory that was transfered to Ukraine for administrative reason. When Ukraine got his indepedance it was implied that it could keep it as long they do not became ennemies from Russia.
Neutrality was deemed acceptable.
Russia took it back in order to prevent the NATO from using it as a major naval base.
As for Abkhazia and South Ossetia, this is not really an invasion. These states wish to be independant from Georgia. Georgia tried to force them to submit by force, they were protected by Russia.
Many of their citizens got a russian passport.
Russia actions are mostly to keep NATO in check.
NATO broke their promises to never under any pretext include former soviet countries.
5) I don't have an opinion about the "illegal drillings". But it is safe to assume that controlling so much oil was alluring.
Moreover USA first implied their neutrality when Saddam prepared his invasion.
6) Germany did wish to integrate german minorities. Moreover Czechoslovakia had also a great military-industrial complex. One of the best in all Europe.
Naturally, they got both under control.