A little bit about the original Indo-European language

No new information here for people well-versed in the subject, but it's a nice introduction to those that want a simple answer to what exactly the original Indo-European language probably was, and especially how the original language can be reconstructed (which I've put in bold). This is from The Languages of the World by Kenneth Katzner.

Who were the original Indo-Europeans, and when and where did they live? Since they left no written documents or artifacts of any kind, our only recourse is to attempt to reconstruct their language. If we assume that a word that is similar in most of the Indo-European languages designates a concept that existed in the original Indo-European society, and that, conversely, a word that varies in most Indo-European languages designates a concept not discovered until later, we may draw certain tentative conclusions. It would appear that the Indo-Europeans lived in a cold northern region; that it was not near the water, but among forests; that they raised such domestic animals as the sheep, the dog, the cow, and the horse; that among wild animals they knew the bear and the wolf; and that among metals they probably knew only copper. Many believe that it was the use of the horse and chariot that enabled them to overrun such an enormous expanse of territory.

The general consensus is that the original Indo-European civilization developed somewhere in eastern Europe about 3000 BC. About 2500 BC it broke up; the people left their homeland and migrated in many different directions. Some moved into Greece, others made their way into Italy, others moved through Central Europe until they ultimately reached the British Isles. Another division headed northward into Russia, while still another branch crossed Iran and Afghanistan and eventually reached India. Wherever they settled, the Indo-Europeans appear to have overcome the existing population and imposed their language upon them. One must conclude that they were a most remarkable people.

The possibility of so many languages having descended from a common ancestor was first suggested in 1786, though the similarity of Sanskrit and Italian was noted as early as the 16th century. By 1818 more than 50 separate languages were established as Indo-European; Albanian was added to the list in 1854 and Armenian in 1875. The total number of Indo-European speakers is about 2 3/4 billion people, nearly half of the earth's total population.