When did the act of privateering officially end?

Answer 1

In 1854 France and England agreed not to use privateers in the Crimean War. In an annex to the peace treaty to end that war, the Treaty of Paris of 1856, the major European powers (about eight countries) agreed not to use privateers. The annex was open to subscription by other countries. By 1880 most maritime powers, with the exception of the United States, Spain, and Mexico, had signed the annex. Use of privateers during the Confederate war was thus legal as the provisions of the treaty only applied to conflicts between signatory powers.

It was not until the second Hague Convention in 1907 that the United States agreed to a convention in which privateering was outlawed. However, before that in 1899, the United States Congress had passed a law which prevented the payment of a bounty to private parties for the seizure of a ship. For the United States the law of 1899 effectively ended the potential of using privateers.

Thus there is no clear date on which privateering officially ended. Presumably, non-signatories to the Second Hague Convention of 1907 might still use privateers. Since there are only 118 countries that have signed this agreement, and about 193 members of the United Nations, it would appear to be a number of countries still capable of using privateers. Among the more notable non-signers are Argentina, Peru, Mauritius, and India.