[4]: 552  Although this went against the main tenet of the Monroe Doctrine (European non-intervention in the Americas), the United States was not in a position to offer much opposition as it was engulfed in its own civil war.

The stalemate between the Mexican political parties, both of whose actions depended on the support of the said European nations and the United States, resulted in a six-year civil war and rendered the country bankrupt.

[5] Earlier in May the English navy had disembarked a 400-men strong contingent at San Blas to secure the Mexican Pacific coast custom houses.

The same year Juárez also crossed the line by illegally seizing 1,100,000 pesos at Laguna Seca that constituted the property of mainly western European merchants.

Such French nationals included a tailor in Mexico City, who had been stabbed in front of his house; a bootmaker who had been robbed and seriously wounded; the relatives' of a Frenchman who was assassinated at Puebla allegedly by the Mexican police; a hotel-keeper who had been robbed twice at Palmar; a farmer who was killed in Durango; a coach-driver who was kidnapped and held for ransom several times; a colporteur who was murdered at Cuernavaca and numerous other instances of robbery, torture or ill-treatment of French subjects in Mexico.

[8] The United States regarded the claims as unjustifiable or even outrageous, except for those of the British;[2]: 70  however the American government offered to cover the arrearages of the debt.

[9]: 22–23  The U.S. remained neutral, but reserved its right to mobilize and intrude upon Mexican soil on behalf of the safety of its citizens and commercial sphere of interest, if necessary.

[9]: 33  These incidents had the potential to escalate into a full-on military conflict between the two nations[2] : 73 [9]: 10  and thus Britain, not wishing to engage in with war with the United States or causing her offence, decided to reduce its naval presence in the expedition.