Aside from low birthrates and high deathrates, what can cause a country's population to decline?

Emigration from a country.

The investiture controversy began as a power struggle between pope gregory vii (1072–85) and henry iv, holy roman emperor (1056–1106).[2] a brief but significant struggle over investiture also occurred between henry i of england and pope paschal ii in the years 1103 to 1107, and the issue played a minor role in the struggles between church and state in france, as well.by undercutting the imperial power established by the salian emperors, the controversy led to nearly 50 years of civil war in germany, and the triumph of the great dukes and abbots. imperial power was finally re-established under the hohenstaufen dynasty. historian norman cantor:

Unique question.well, using science, you cannot create or destroy even if you do eat yourself so you would not grow twice as big, nor would you disappear. you would stay the same but change states potentially, or at least change your appearance (obviously).hope this . keep up these unique questions.