The decline of the Roman Empire lead to disorder everywhere in western Europe. Many of the Germanic invaders were too weak to govern well. As a result, towns and villages fell into ruin. Roads and bridges were not repaired. Robbers roamed the countryside, making it unsafe for travelers. Trading and business slowed down, and there were shortages of food and other goods. People were no longer interested in learning, and many books and works of art were damaged or lost. For these reasons, this time is also sometimes called the "Dark Ages" by historians.
During the 900's, Charlemagne's empire and Anglo-Saxon England were attacked by new invaders known as Norseman, or Vikings. They came from the far northern part of Europe in an area now called Scandinavia. the tall, fair-skinned Vikings were brutal fighters and robbers. They spread fear and destruction throughout western Europe for several hundred years. However, they opened up new trade routes and taught seafaring skills to other Europeans.
The Vikings captured parts of Britain and France. They ruled cities in Russia and set up colonies on islands in the North Atlantic. They even paid a visit to North America. Those who went abroad married the people they conquered and excepted a new religion and new customs. Others stayed in Scandinavia and set up the kingdoms of Norway, Sweden, and Denmark.
Central government collapsed after the death of King Charlemagne. Power passed from kings to local lords, giving rise to a system known as feudalism. Under feudalism, landowning nobles governed and protected the people in exchange for services, such as fighting in a noble's army or farming the land. With western Europe divided into thousands of feudal territories, the Church served as a unifying force and exerted a strong influence over the culture of the Middle Ages.
In 1071, under the guiding influence of the Church, Europeans began a series of wars which lasted over 200 years. These wars were called the Crusades, and hundreds of thousands were killed in the name of God. Misguided Christian crusaders killed Christians, Jews, and Muslims alike - the Pope had told the Crusaders that any sins committed during the "holy war" would be forgiven.
The growth of trade and towns during the late Middle Ages led to many changes in western Europe. Some of these changes were political. The rise of monarchies, or countries governed by one ruler, led to the end of feudalism.
http://www.castles.org -Lots of pictures of castles.
http://www.castlesontheweb.com - Great castles.