How does desertification happen?

Overgrazing of drylands is a big one. An immediate reason is the removal of vegetation. This is caused by a few things like drought, climate change, tillage, deforestation, and overgrazing. 

Desertation is the accumulated results of ill-adapted land use and the effects  Dersertification is the accumulated results of ill-adapted land use of a harsh climate. For human and nature represent the most immediate causes:
over cultivation
overgrazing
exhaust the soil
deforestation
poor drained irrigation
land degradtion.

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:

Place the point of the compass on point b and draw an arc that intersects  be¯¯¯¯¯  , using    ab    as the width for the opening of the compass.  hope it