The Viking Kingdoms of Scandinavia Were So Successful Because

The Viking kingdoms of Scandinavia were so successful because:

A) they continued to rely on traditional Viking networks of trade and kinship but combined them with newer models of governance.
B) their legitimacy was immediately recognized by other polities,which feared the Vikings would attack them if the kingdoms were not recognized.
C) they refused to convert to Christianity or to recognize Christian kings as legitimate.
D) they like the Roman Empire,they relied heavily on a slave economy.
E) they remained isolated and uninvolved in European affairs.