The political structure of Western Europe changed with the end of the united Roman Empire. Although the movements of peoples during this period are usually described as "invasions", they were not just military expeditions but migrations of entire peoples into the empire. Such movements were aided by the refusal of the western Roman elites to support the army or pay the taxes that would have allowed the military to suppress the migration. The emperors of the 5th century were often controlled by military strongmen such as Stilicho (d. 408), Aspar (d. 471), Ricimer (d. 472), or Gundobad (d. 516), who were partly or fully of non-Roman background. When the line of western emperors ceased, many of the kings who replaced them were from the same background. Intermarriage between the new kings and the Roman elites was common. This led to a fusion of Roman culture with the customs of the invading tribes, including the popular assemblies that allowed free male tribal members more say in political matters than was common in the Roman state. Material artefacts left by the Romans and the invaders are often similar, and tribal items were often modelled on Roman objects. Much of the scholarly and written culture of the new kingdoms was also based on Roman intellectual traditions. An important difference was the gradual loss of tax revenue by the new polities. Many of the new political entities no longer supported their armies through taxes, instead relying on granting them land or rents. This meant there was less need for large tax revenues and so the taxation systems decayed. Warfare was common between and within the kingdoms. Slavery declined as the supply weakened, and society became more rural.[F]
The loss of what led to the differentiation between the Western Roman Empire and the new kingdoms? (If the question is unanswerable, say "unanswerable")
tax revenue