The Belfast was a British ship that was seized by the United States in 1868. The ship was carrying a cargo of arms and ammunition that was intended for the Irish Republican Brotherhood, a group that was attempting to overthrow the British government in Ireland. The United States government argued that the shipment was in violation of the Neutrality Act of 1794, which prohibited the shipment of arms and ammunition to foreign countries. The case was brought before the Supreme Court of the United States, which ruled in favor of the United States government. The Court held that the Neutrality Act of 1794 was still in effect and that the shipment of arms and ammunition to a foreign country was in violation of the Act. The Court also held that the United States had the right to seize the ship and its cargo in order to enforce the Act. The Belfast case was an important decision in the history of the United States. It established the principle that the United States government had the right to enforce its neutrality laws and to seize ships and cargoes that were in violation of those laws. The decision also established the principle that the United States government had the right to protect its citizens from foreign interference.

In The Belfast, 1868, the Supreme Court issued a dissenting opinion that highlighted the importance of international law in maritime disputes. Justice Field argued that under international law, neutral vessels have an absolute right to be free from capture and detention by belligerents during times of war. He noted that this right is so fundamental to international relations between nations that it should not be subject to any exceptions or limitations imposed by domestic courts. Furthermore, he stated that even if there were some circumstances where such captures could be justified under domestic laws, they would still violate established principles of public law and thus remain unlawful according to international standards. In conclusion, Justice Field asserted his belief in the supremacy of international over domestic laws when dealing with matters concerning foreign countries and their citizens on the high seas.