Complex sentence: At each stage, the efficiency brought by the new methods rendered old methods obsolete and unable to compete economically, resulting in a centralisation of mining, especially in regions where power (the principle operating expense) is cheaply available.
Split into simpler sentences: At each stage, the efficiency brought by the new methods rendered old methods obsolete and unable to compete economically. The result of this process was a centralisation of mining, especially in regions where power (the principle operating expense) is cheaply available.