One basic demographic problem of the period was how to make a correct assessment of Macedonia's population by nationality. This was an impossible target, given the constant shifts in administration and the intentional fabrications on the part of census takers and respondents alike.
At the start of the 20th century, the Christians (Greek-, Slav-, Albanian- and Vlach-speaking) appeared to constitute the majority of the population of Macedonia (which was more than 1.5 million), but their percentage began to drop as a result of emigration to Bulgaria and the United States (chiefly by Slav-speakers).
The total percentage of Muslims in Macedonia continued to shrink, however, despite the on-going settlement of Muslim refugees from the northern Balkans, as the Ottoman Empire lost territory.
During the same period, unrest in the countryside combined with the development of industry caused peasanats to flock to the cities at high rates. They preferred the administrative centers, but also chose locations close to the railway lines. In these places, as in the zone south of the imaginary line that unites Kastoria with Edessa and Serres, the Greek language was overwhelmingly predominant.