Final answer:
France's attempt to build a canal in Panama failed mainly due to local resistance and diseases, particularly yellow fever and malaria, which caused over 20,000 deaths and led to the project's financial collapse.
Step-by-step explanation:
The main reason France failed to build a canal in Panama was due to local resistance and diseases. Despite having experienced engineers like Ferdinand de Lesseps and later Gustave Eiffel, the project was plagued by tropical diseases such as yellow fever and malaria. The harsh conditions, coupled with relentless tropical rains, flooding, and mudslides, resulted in the deaths of over 20,000 workers, leading to economic ruin and the project's eventual bankruptcy within eight years after excavation began.
Moreover, the French encountered a daunting tropical climate and swampy terrain, which further exacerbated the spread of diseases among the workers. In contrast, when the United States took over the project, they first focused on eradicating the mosquito population that spread malaria and yellow fever, utilizing chemicals like DDT and improving medical and infrastructure conditions to support the workforce. This allowed them to successfully complete the Panama Canal in 1914, overcoming the challenges that had doomed the French effort.