Germany and Japan seriously underestimated Americans ability to ?

They underestimate America ability to produce weapon.

Explanation:

This underestimation occurs during the WW 11 where the country of Germany and Japan look down of America ability to produce weapons to fight during the war. They underestimate America ability to produce war armory like ships, airplane, vehicle in a fast moment to fight against them during the war.

They also underestimate them being unable to increase the number of their Merchant Marine of the U.S navy to provide assistance to the U.S and to some of her allies.

pepin the short[a] (german: pippin der kurze, french: pépin le bref, c. 714 – 24 september 768) was the king of the franks from 751 until his death. he was the first of the carolingians to become king.[b][2]

the younger son of the frankish prince charles martel and his wife rotrude, pepin's upbringing was distinguished by the ecclesiastical education he had received from the monks of st. denis. succeeding his father as the mayor of the palace in 741, pepin reigned over francia jointly with his elder brother carloman. pepin ruled in neustria, burgundy, and provence, while his brother carloman established himself in austrasia, alemannia and thuringia. the brothers were active in suppressing revolts led by the bavarians, aquitanians, saxons, and the alemanni in the early years of their reign. in 743, they ended the frankish interregnum by choosing childeric iii, who was to be the last merovingian monarch, as figurehead king of the franks.

it proved indian land claims were unjustified.