During military campaigns in the 19th century many soldiers died of diseases. Why did the military leaders not seem to pay as much attention to the importance of supply to the army? Let me give some examples
1) In 1802 France sent soldiers to crush the rebels on Haiti. But the campaign failed because almost all of the soldiers died of disease.
2) British invasions of the River Plate (Spanish Argentina) in 1806. The invasion failed because of disease.
3) Finally the French Egypt Campaign 1798-1801 many French soldiers died of plague but why did many of the locals and the Ottoman soldiers not die? And why didn't the French take the measures that the others did to prevent plague?