Which event resulted in president johson sending additional troops to vietnam without a formal declaration of war?

The answer would be : Gulf of Tonkin Incident

Explanation:

The incident became really complicated because both side of Vietnam and United states claimed that they were being attacked first. According to US' report, the ships from the northern Vietnam were the first one who opened the fire. Using this report as a basis, in the end President Johnson action was justificated  

the french gave their support to another tribe during he war.

they died because of a disease during the first spanish colonies.