Why Did Roman Diplomats Help Some German Chiefs Consolidate Tribes

Why did Roman diplomats help some German chiefs consolidate tribes into kingdoms?

A) to help stabilize turbulent regions and raise up leaders with whom Rome could negotiate lasting treaties
B) in order to ensure that the German kingdoms would be a deterrent to a potential Hun advance
C) as a strategy of divide-and-conquer whereby Rome could pick off weak German kingdoms
D) because the Roman diplomats were German by nationality and wanted to help their own
E) because kingdoms made better trading partners for each other,freeing Rome from contact with them