This blog post is the result of a thought-process which started after reading the phrase "Wars will be obsolete", at the back of "Homo Deus", a book I'm currently reading, written by the very talented Yuval Noah Harari.
Our history is filled with wars. The good news is that this will probably change in the next 20 to 30 years.
A war is most of the time purely economically-driven. Otherwise, there wouldn't be any reason to put so much effort into invading another country. With globalization though, this economical "incentive" to start wars loses most of its value.
The reason why the US hasn't started a (real) war against China for example, is because neither of these countries have anything to win in a fight against each other.
Aside from that, it's also worth considering that with the tools these nations have, starting a war, means the nearly instant destruction of both of these regions. This is mainly because of the emergence of nuclear weapons in the 20th century.
Finally, once the regions where there are still wars evolve (such as Syria, Afghanistan, and regions with regular tensions such as Africa), the world will become a network of economically linked entities, which have nothing to win in attacking each other. Wars (like we know them) will effectively have become obsolete.