Answer: Check Explanation Below
Step-by-step explanation:
The Concert of Europe, known as Europe's congress system started off with the Congress of Vienna. Vienna is the capital city of Austria, a country in Europe. It contained 4 big empires at the time, United Kingdom, Austria, Prussia and Russia. These empires met at times of crisis to unite the continent of Europe.
Later on, the Concert expanded on to France, but then the year 1848 came, and there were revolutions across the continent, ending the concert for now.
It came back again a couple of years later, added Italy & Germany to it and Austria became Austria-Hungary. But this wouldn't last too long either because different empires in the concert started forming alliances and empires started colonizing parts of Africa, Asia and the Americas, so their focus on the concert had reduced.
The last straw of the concert happened early 20th century, when Franz Ferdinand of Austria-Hungary was assassinated by a Serbian Nationalist is Bosnia-Serbia and complete havoc swept across the world, starting WWI. The concert could no longer unite Europe, and Europe was never the same after the two World Wars.
Hope that helped a lot.
:)