The London Stock Exchange Group, one of the oldest and largest stock exchanges in Europe, announced the largest transaction in its storied history Thursday with its $2.7 billion acquisition of the Russell 2000 Index.

The Russell 2000 is a small-cap stock market index owned by Seattle-based asset management firm Russell Investments, formerly known as the Frank Russell Company after its founding family, which sold the business for $1.2 billion in 1999 to the Northwestern Mutual Life Insurance Co.