Final answer:
The first year of the United States building the Panama Canal was unsuccessful mainly due to a yellow fever outbreak, which caused high mortality among workers and had been a major issue during the French attempt as well.
Step-by-step explanation:
The reason the first year of the United States building the Panama Canal was unsuccessful was primarily due to the yellow fever outbreak. The tropical disease, along with malaria, posed significant health risks and led to high mortality rates among workers. This was a continuation of the same issues the French encountered during their failed attempt to build the canal.
The United States addressed this by sending civil engineers and medical professionals to Panama to eradicate the mosquito population, thereby controlling the diseases that were causing such high worker turnover. It was a daunting task, but the implementation of fumigation systems and mosquito nets, following Dr. Walter Reed's discovery of the role of mosquitoes in the spread of malaria and yellow fever, eventually helped to reduce the death rate. This improvement in health conditions allowed for the continued construction of the canal, which was completed in 1914, becoming a monumental engineering feat that significantly influenced world trade and military defense patterns.