Today, a large part of the world considers itself to be the part of Western civilization. We're talking about Europe, Russia, the Americas, Australia, New Zealand, and even more areas, where people live by the same or similar cultural standards. Although some other great, old and mighty civilizations exist, the Western civilization has been the impetus of economic and social progress for last 500 years (not always in a fair way, we have to admit). So, what actually led to the world we live in today?
It all started on the European continent, actually in Greece, when the city state of Athens decided to implement democracy in 6th century BC. It was a weird form of democracy; it allowed slavery and it was also forbidden for women to vote, only the free men were allowed to do it. But still, it seems to be some kind of progress towards today's democracy.
Greece's political power declined, but the culture was largely inherited by Romans. Their empire was the pillar of western civilization for some 600 years. At some point - as every society does - it became extremely decadent, and it needed some "refreshment of moral values", so the Christianity was accepted by all social classes in 313 A.D. Thanks to that, the empire lasted to 492 A.D., when barbaric German tribes from the north captured the city of Rome. The empire collapsed, but the barbarians also accepted Christianity, and in the upcoming years, the majority of Europe adopted some form of merged Christian - barbaric culture. The barbarians I'm talking about are of Germanic, Slavic, and Celtic origin. Let's not forget to mention that the eastern part of the empire survived for another 1000 years as Byzantine empire, and was ruled by Greeks again.
The Western civilization could have been ended by Muslims from Northern Africa, who conquered Iberian peninsula (today's Spain and Portugal), but Muslims were defeated by joint west European armies at Tours, France, in 732, and later expelled from Iberia by Spanish Inquisition. And what follows is one of the major turning points of world's history: Spanish court financed Christopher Columbus to do some exploring, and so he accidentally (re)discovered the New World in 1492. After that, almost all countries from Western and Northern Europe established colonies there, and that also brought some bad things with it: destruction of native cultures, re-emergence of slavery and exploitation of European colonists.
It is natural for repressed people to rebel, and in 1776, 13 colonies in America declared independence from British crown. De facto, USA was created, and from that time, it represents a pillar of today's Western civilization, the first and the strongest one out of European continent. Around that time, in 1789, the French revolution also took place. The French citizens have overthrown the king and his government, and reserved political power for themselves with a motto: freedom, equality, brotherhood! They created a republic of free citizens, and contributed well to the establishment of freedom and democracy as we know them today. They spread the idea throughout all Western world. Another great step towards the world we know was abolition of slavery in the U.S. after Civil war. Well, we can say that today the U.S. is contributing a lot to shape the Western culture: after 1915 it helped to end two senseless wars, and it is the greatest Western political and economical power, and with it's influence largely shapes the world we live in.
We can conclude that the cradle of today's Western civilization definitely is the European continent, from ancient Greece through Roman empire to middle ages and colonial era. But after its end, for the last century, we must consider U.S. to be the strongest base of Western civilization.