Answer:
it's defense of human rights
They wrote a new constitution in 1917 after a 7 year revolution against the former government. the constitution made many changes and the first constitution that was given social rights, rights for healthcare, the right for a place to live and lastly the right to work in any occupation that you want. all these right were given to the people of mexico.
hope this helps.
I think it has something to do with dry crops.
