Accession (noun)

The act of coming to a position of power or authority; the act of becoming a member of a group or organization.

Origin:

From latin accessio, from accedere to come near.

Examples:

1. His accession to the throne was met with great celebration.
2. Her accession to the presidency was historic.
3. The company's accession to the trade association was a positive development.
4. The country's accession to the European Union was a long process.
5. The team's accession to the league was a result of hard work.