I think deluded Jews pictured black men with machine guns defending them and going to war on their behalf. They think blacks could be bought as mercenaries. It is a cowardly instinct that some people have to think of ways to get other people to do their dirty work for them (probably because we see that many american blacks have a knack for violence and little aversion to it).
The Jews who fund black causes think there is some sort of quid-pro-quo...We'll give you money, and you risk your life to fight for us if things go down.
As allies I don't think we've gotten a very good return on investment.
Maybe best to learn to do your own dirty-work by your own hand.
All that said, I don't mind a lot of black people. I just don't harbor any illusions that they want to die fighting for Jewish causes nor do I think merceneries are a good choice for any Jewish cause.
Any nation that has employed mercenaries for their defense force usually falls, Egypt was known for using mercenaries, and many nations used Germans as mercenaries. I don't know if the kingdom of Israel employed mercenaries, I think they had a militia that was called to raise arms when the time was needed and every male was required to be armed but I don't think they had a standing military.