"The deed is history, its sign remains."
(Ovidius)
Due to geographical separations the Germanic peoples eventually developed some small cultural differences that resulted in a northern group, a western group, and an eastern group; this three groups were still very closely related to eachother and could even understand eachothers language without much problems, during the Middle Ages the differences between the Germanic tribes slowly became bigger; some tribes remained free while others were subjected by Medieval kingdoms, some were Christianized while others were not, some were influenced by other cultures, others were torn apart by a border that was drawn through their land and some tribes mixed with the local inhabitants of the foreign area they had settled in.
Discord among the tribes:
As you can see there are many reasons for the eventual disappearance of the Germanic cultural unity, one of the main reasons for this was the lack of political unity between the tribes, while the Germanic peoples were certainly aware of their mutual kinship they never managed to unite completely due to internal conflicts and discord; almost every tribe had its own king and many tribes fought bitter wars with eachother, the only thing that could unite the tribes for a brief amount of time was a common threat that had to be fought, and after the threat had been dealt with most tribes left the coalition again.
Because of their internal discord they could sometimes easily be subjected by foreign powers that quickly Christianized them and absorbed them into their empires, one by one the tribes were slowly defeated this way.
New cultures:
Another reason for the disappearance of the independant tribes was the Medieval feudal system; many nobles were given a piece of land by their kings and this land was often simply created by drawing a border somewhere on a map without any consideration for the cultural, religious, and linguistical differences in that area; in this way many countries were created in which multiple peoples, religions, cultures, and languages resided, most of the time this caused internal conflicts and discord that the local rulers tried to quell by uniformizing all aspects of the country so that there were no differences to quarrel about anymore, this tactic was also used in the United States where the early colonists with their different cultural backgrounds were united under values like Freedom and Christianity; individual opinions about this subject are irrelevant on this page, I'm mainly bringing up this subject to show that the process of uniting different cultural groups under a new culture will cause the former cultures to slowly fade away.
This process also took place in Medieval Europe, which eventually scattered the Germanic tribes and caused them to lose their former cultural unity.
Land-swopping:
Because of the many wars that were fought during the Middle Ages most areas continuously changed hands, I am not exaggerating when I say that some areas had a new ruler almost every year, kings played with countries as if they were toys, which eventually resulted in a patchwork of hundreds of little states that were scattered all over the map of Europe; peoples and countries were ripped apart and most of our modern borders have been established during this rough times.
Did the Germanic culture simply disappear? of course not... the cultural heritage of our ancestors is still alive today and can be seen all around us, it lives on in our modern holidays, legends, customs, languages, and other aspects of our lives; we can choose to ignore this, but aren't we throwing away our own roots then? without knowing our ancestors we are orphans, our ancestors are alive within us and we ourselves choose whether we wish to learn from them or not.
Another reason for the disappearance of the independant tribes was the Medieval feudal system; many nobles were given a piece of land by their kings and this land was often simply created by drawing a border somewhere on a map without any consideration for the cultural, religious, and linguistical differences in that area; in this way many countries were created in which multiple peoples, religions, cultures, and languages resided, most of the time this caused internal conflicts and discord that the local rulers tried to quell by uniformizing all aspects of the country so that there were no differences to quarrel about anymore, this tactic was also used in the United States where the early colonists with their different cultural backgrounds were united under values like Freedom and Christianity; individual opinions about this subject are irrelevant on this page, I'm mainly bringing up this subject to show that the process of uniting different cultural groups under a new culture will cause the former cultures to slowly fade away.