KAMPALA, Uganda (AP) — A new study by two British universities says Somalia’s piracy problem can be sustainably solved by building roads and harbors to encourage people in remote areas to engage in legitimate trade.

The study by Oxford University and King’s College London says Somali clans do not offer protection to pirates if they have a steady stream of income from taxing trade in their ports and markets.

Piracy off Somalia’s coast has been declining thanks largely to a heavy but costly international military presence in the Indian Ocean.

More than 100 hijackings have taken place since 2005, according to the World Bank, which says naval law enforcement interventions may not be sustainable in the long run. The bank said last year that focus needs to be shifted from perpetrators to enablers.

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