It is difficult to spread democracy because it has to result from D. Domestic politicswithin those countries
Democracy cannot workunless the societal norms and politics in the specific country support it. This is why giving nations that are used to dictatorships and monarchies, democracy, might result in them going back to their less than democratic old systems of government.
The other options are wrong because:
Interstate war has been proven not to work as seen Vietnam war where the North Vietnamese resisted democracy
Intrastate war has also proven not to work as seen by the Afghan Civil War that ended in victory for the Taliban.
Treaties have also failed to work as shown by China renegading on the treaty it signed with Britain not to interfere in Hong Kong for a period of time.
In conclusion, democracy can only work when the domestic politics of the country supports it.
