Its objective was to declare that the New World and the Old World to be separate entities. It opposed European colonialism in the new world. The Latin American countries were gaining independence from Spain and Portugal. The US was worried there would be new attempts by Old World countries to try and interfere with or try to conquer the newly independent territories and it would become a battleground. The doctrine was declared this. wouldn't be tolerated. The New world wanted to be left alone to exert its influence.
The threat of France possibly spreading the its monarchial government was a catalyst
It has a big impact on how a message is received it is false
In 1919, Germany had just emerged as the loser of World War I, meaning that as a condition of their surrender they were forced to creat a new government that wasn't involved in the destruction of the past.
Usually its the Custodian, as he is the last to leave.
I hope this helps! :)