▁the ▁San ▁Francisco ▁Bay ▁Area , ▁and ▁possibly ▁responsible ▁for ▁the ▁July ▁ 1 9 1 6 ▁Black ▁Tom ▁explos ion ▁in ▁New ▁Jersey , ▁was ▁based ▁in ▁Mexico ▁City . ▁The ▁failure ▁of ▁United ▁States ▁troops ▁to ▁capture ▁Pan cho ▁Villa ▁in ▁ 1 9 1 6 ▁and ▁the ▁movement ▁of ▁President ▁Car ran za ▁in ▁favor ▁of ▁Germany ▁emb old ened ▁the ▁Germ ans ▁to ▁send ▁the ▁Z imm ermann ▁note . ▁ ▁The ▁German ▁provoc ations ▁were ▁partially ▁successful . ▁President ▁Wood row ▁Wilson ▁ordered ▁the ▁military ▁invasion ▁of ▁Ver ac ru z ▁in ▁ 1 9 1 4 ▁in ▁the ▁context ▁of ▁the ▁Y p ir anga ▁Inc ident ▁and ▁against ▁the ▁advice ▁of ▁the ▁British ▁government . ▁War ▁was ▁prevent ed ▁thanks ▁to ▁the ▁Ni ag ara ▁F alls ▁peace ▁conference ▁organized ▁by ▁the ▁ABC ▁nations , ▁but ▁the ▁occupation ▁was ▁a ▁decis ive ▁factor ▁in ▁Mexican ▁neutral ity ▁in ▁World ▁War ▁I . ▁Mexico ▁refused ▁to ▁particip ate ▁in ▁the ▁embargo ▁against ▁Germany ▁and ▁granted ▁full ▁guarante es ▁to ▁the ▁German ▁companies ▁for ▁keeping ▁their ▁operations ▁open , ▁specifically ▁in ▁Mexico ▁City . ▁These ▁guarante es ▁last ed ▁for ▁ 2 5 ▁years ; ▁coinc ident ally , ▁it ▁was ▁on ▁ 2 2 ▁May ▁ 1 9 4 2 ▁that ▁Mexico ▁declared ▁war ▁on ▁the ▁A xis ▁Pow ers ▁after ▁the ▁loss ▁of ▁two ▁Mexican - flag ged ▁tank ers ▁that ▁month ▁to ▁Kriegs marine ▁U - bo ats . ▁ ▁German ▁motiv ation ▁for ▁the