Mackenzie also sent a letter to a newspaper called The Buffalo Whig and Journal asking for troops from the United States. On December 7, government forces arrived at Montgomery's Tavern and fired towards the rebel position. Mackenzie was one of the last to flee north, leaving his papers and cloak behind. He met with rebel leaders who agreed the rebellion was over and that they needed to flee Upper Canada. Bond Head issued a warrant and a £1,000 () reward for Mackenzie's apprehension. Mackenzie travelled to the Niagara River and entered the United States by boat. Attempted invasion from the United States Mackenzie arrived in Buffalo on December 11, 1837, and gave a speech outlining his desire for Upper Canada to be independent of Britain. He blamed the failed rebellion on a lack of weapons and supplies. Josiah Trowbridge, Buffalo's mayor, and a newspaper called the Commercial Advertiser interpreted the speech as a rallying cry for help with the rebellion. On December 12, Mackenzie asked Rensselaer Van Rensselaer to lead an invasion of Upper Canada. Van Rensselaer would lead Patriot forces, composed of volunteers who sympathized with the cause and were living in the United States. Rebel leaders chose Van Rensselaer because the Van Rensselaer family name would bring respectability to their campaign, his father had been a successful military general in the War of 1812, and he claimed to have military experience. Van Rensselaer, Mackenzie and 24 supporters occupied Navy Island on December 14 and Mackenzie proclaimed the State of Upper Canada on the island, declared Upper Canada's separation from the British Empire, proclaimed himself appointed chairman of its new government and wrote a draft for the constitution of the new state. Van Rensselaer planned to use the island as a staging point to invade the Upper Canadian mainland, but this was stopped when their ship, the Caroline, was destroyed by British forces in the Caroline affair. On January 4, Mackenzie travelled to Buffalo to seek medical help for his wife. On the way he was arrested for violating the Neutrality Act, a law that prohibited participating in an invasion of a country against which the US government had not declared war. He was released on $5,000 () bail, paid by three men in Buffalo, and returned to Navy Island in January. British forces invaded the island on January 4, 1838, and the rebels dispersed to the American mainland.