Which factor, self-interest or idealism, was more important in driving american foreign policy in the years 1895-1920?

This time period really should be differentiated.  The early part of the period was dominated by self-interest while the end of the period had aspects of idealism about it.  Overall, I would argue that self-interest predominated, but it would be much clearer if we separated this period into the WWI Era on the one hand and the time before it on the other.

The early part of this time period is dominated by the Spanish-American War and the Roosevelt Corollary to the Monroe Doctrine.  These things showed the US doing things like occupying ore even taking other countries (Nicaragua, the Philippines) to promote its own interests.

The WWI era is dominated by Woodrow Wilson and the Fourteen Points.  Wilson's goal was to create a world order that would be conducive to peace.  This is a much more idealistic motive than was present in the early 1900s.

Overall, I would argue that the self-interest predominated, but that idealism came more to the fore at the end of the period.

doesn't make any since

explanation:

workers of lowell mills were greatly benefited for the waltham type of work which was more a paternalist kind, trying to protect the integrity of this little girls coming from small farmers and providing an adequate place of work, this in an effort to avoid the issues of bad place conditions and immorality that the people in bigger industrialized cities of great britain were experimenting.