An Anglo-Dutch maritime treaty with Tokugawa Japan

How would an early treaty letting Dutch and English forces police Japanese waters in exchange for technology affect the American Black Fleet?

Japan would be less isolated, might possess a functioning navy, and could enjoy British or Dutch backing, making an American demand to open the country much harder to justify or enforce.

The answer focuses on the political and naval assumptions behind gunboat diplomacy. If Japan already traded with European partners and maintained a navy through sustained technical exchange, the United States could not present itself as simply opening a closed country and would face a more credible local and international response.