When business mergers, acquisitions and amalgamations should be envisaged ? Is it fair if such act leads to monopolistic market ?

Depending on what country the result of the Merger or Acquisition has is localized, "fairness" as to monopolistic markets are governed by the relevant anti-competition or anti-trust laws.

They usually happen when companies are aiming to grow. They must be aligned to the ccompany's strategy to yeild the sought results.

Laws and regultation should be deviced to prevent monopolistic acts in oder to prevent such actions, and some countries do that.