Saudi Arabia, Turkey, and Pakistan’s new defense pact is already attracting interest from Bangladesh, Egypt, and Iran. But expansion could reshape regional security, alliances, and power balances. By GIORGIA VALENTE Less than three weeks after Saudi Arabia , Turkey , and Pakistan signed the Mecca Joint Defense Agreement, attention is shifting from the pact’s collective defense pledge to a more consequential question: Who else might join it? Bangladesh has publicly expressed interest, Egypt says it is studying the prospect, and Iran, arguably the most consequential possible addition, has found itself at the center of conflicting reports. An Iranian parliamentary media official said Tehran had received an invitation, but the Foreign Ministry later said no official invitation had been delivered. The uncertainty is significant because enlargement could determine whether the Aug. 7 agreement remains a trilateral security arrangement linking three major Muslim powers or dev...