As Is Evident When Examining the Experience of Enlisting Foederati

As is evident when examining the experience of enlisting foederati into the Roman Empire,when are foreign allies most likely to contribute to the military interests of the host nation?

A) when their own lands are being threatened
B) if coerced into these actions
C) when they feel incorporated as equals into the host society
D) if an effective assimilation campaign is undertaken
E) if the enemy being fought is a common enemy to both groups