AMCOS has reciprocal agreements with other affiliated societies around the globe – meaning you reproduction royalties are collected worldwide.
Some territories overseas require individuals to set themselves up as a Publisher or use a third-party music service to collect 100% of reproduction royalties, but as an AMCOS member you do not need to do this.
If all your songs or compositions are published, your music publisher will collect your reproduction royalties, and there's no reason to join AMCOS. AMCOS is primarily a royalty collection service and does not play the role of a music publisher. Find out what a music publisher does.