Topic is monroe doctrine:
what did it state?
why was it written?

Principles of Monroe Doctrine (1824) were mentioned by the president James Monroe in his speech in Congress already in 1823:

1) American continent is not going to be object of colonization  of any of European powers

2) political system of American states differ from political system of European powers. USA will consider whatever attemp of European powers to broaden European system in whichever part of the globe as a threat of peace and American security.

3) USA is not going to intervene to today´s European colonies

4) USA is not going to interfere  to European affairs and Europeans wars.

Explanation:

One of the consequences of Napoleonian wars were wars for independence in Latin America. Result of this was very bad for Spain because Spain lost almost all territories in Americas. At the time of Monroe Doctrine Spain owned only Cuba, Portorico and Santo Domingo. In Europe after Congress of Vienna (1814-15) there was a tendency to restore absolute monarchy wherever it was endangered. In Spain, for example, liberals proclaimed constitutional monarchy (1820) but in 1823 French army ( invaded Spain and restored absolute monarchy of Fernando VII. (invasions like that were negotiated  among European powers in so-called "Congres system", i.e. invasion to Spain was negotiated at Verona Congress in 1822). Americans were afraid that "Congress diplomacy" could be applied in ex-colonies in America as well. Americans had their economic interests in Latin American countries and did not want European interventions. Monroe Doctrine was a reaction to Congress policy of European powers.

then its a law the end