Maintaining the loyalty of those you invite to protect you can be a bit tricky - according to one source that's how the Anglo Saxons were invited to what became England to help protect a post Roman society of Britons from attacks from what is now Scotland (Picts and Dalriadic Scots):

https://en.wikipedia.org/wiki/Anglo-Saxon_settlement_of_Brit...

I'd expect the loyalty to a rich employer would last right up to the point where money becomes worthless - after that exactly what bargaining power would a rich person have? Up to a certain point in history you achieved and maintained royal status largely by being a stupendous bad-ass...

The quote: "There is no arguing with the barrel of a gun" springs to mind here. Money means nothing if you don't have the ability to protect it. Interestingly, regulations and the spaghetti mess that is the banking system kinda serve as a means of protection; only certain clerks know the safe pathway in the network of laws and files that otherwise hide dragons of fines and the dreaded lawyers.

There needs to be a sense of shared purpose.

I would think the easiest way would be to start a religious sect, as this would give you non-monetary legitimacy, akin to a modern day Mandate of Heaven or Divine Right of Kings.

Or if religion isn't your flavor, then some type of philosophical/political/national organization. However, I think it works better with religion because of the afterlife component.

It would also be best to get your followers when they're young. So perhaps start an educational fund that helps underprivileged families, with one of the requirements being to study your organization's ideology. Even better would be to fund multiple orphanages and have them run by members of your sect.

The Mormons and Pentecostals will inherit the Earth (or at least LA): https://news.ycombinator.com/item?id=13484925

I wonder if something like the Cartasian Maths from Anathem might work?