Longman was at the time the largest and most profitable UK imprint. Amongst their many successful operations were English as a Foreign Language publishing, medical publishing (Churchill Livingstone), and very successful publishing operations throughout Africa and the Middle East. When there were shocks to the system, as there were when, for instance, government failure in Nigeria caused them to default on a £6 million debt, the company could weather the storm because of diversification.
I fear for the modern Pearson which has put almost all its eggs in the US education market. It has sold off the family silver: Royal Doulton, Chessington Zoo and Chateau Latour went long ago, but more recently they have sold the Financial Times, and their share of The Economist. Now they are to sell their 47% stake in the enormous Penguin Random House. Perhaps it will be in safer hands with Bertelsmann.