The research of this study is to outline the effect of mergers on selected American banks from the period 2005 to 2019. The research study basically uses two methods, first method uses The Pre- and Post-merger monetary performance measurement with the help of financial variables like Earning Per Share, Return on Equity, Return on Assets, etc. PNC Bank and Old National bank had shown positive effects on all the variables using the first method. Capital One Financial Corporation had shown a positive effect on the majority of the variables except for Return on Assets and NBT Bank had also a positive effect on the majority of variables except for Return on Equity and Return on Assets. The second method uses comparative analysis where financial variables of the banks are compared with an average of the respected banks. NBT bank had a negative effect on Earning Per Share compared to the averages of all the respected banks. Old National Bank had also shown a negative effect on earnings per share, Return on Equity & Yield on Advances compared to averages of all the respected banks. Capital One Financial Corporation & PNC Bank had a negative effect on most of the variables using the comparative analysis on variables like Return on Assets, Yield on Investments, Net Profit Ratio, Business Per Employee & Profit Per Employee compared to an average of the respected banks.