Complex sentence: The core constituent was of a merger between the banking firm of S. Bleichröder founded by Samuel Bleichröder in 1803 in Berlin; whose bank maintained close contacts with the Rothschild family acting as a branch office in Berlin of the Rothschilds' bank.
Split into simpler sentences: The core constituent was the banking firm of S. Bleichröder founded by Samuel Bleichröder in 1803 in Berlin. The bank maintained close contacts with the Rothschild family acting as a branch office in Berlin of the Rothschilds' bank.