thoughts:

• convert - try to sign them up to the system i.e. the way religions used to do it. Reason with them and tell them they want to join because it's better.
• kill them - historic wars happened.
• bind them explicitly - society today binds adults to legal responsibility to their own rights. children are not bound in the same way until we say they are capable of being responsible, in a way they are people who won't adopt the system (sometimes because it's too complicated for them). Our solution is to bind others to the responsibility and eventually bind them when they are old enough to adopt the system (18 years old is usually an adult in most countries)
• (an instance of compulsion) threaten them with being cast as an entity with less rights within your system than other entities if they do not join your system.