An act named for this commodity was used by LeicesterHemingway to establish an unrecognized country 
An act named for this commodity was used by LeicesterHemingway to establish an unrecognized country he called "New Atlantis". This commodity's presence on Navassa Island led to a border dispute between the US and Haiti, and slavery (*)  continued to be practiced in mines for this quantity by confederate exiles in the Caribbean after the 13th amendment was passed. This commodity's recent exhaustion in Nauru has led to a budget shortfall that is largely met with Australian aid. This commodity's richness in Phosphates led to its use as a "miracle fertilizer" in the 19th century. For ten points, name this commodity excreted by birds and bats.
An act named for this commodity was used by LeicesterHemingway to establish an unrecognized country he called "New Atlantis".
Guano  (prompt on "manure")