How to build a global business empire in the 21st century

No firm is an island. All strike contracts and compete with others. Conversely, when bosses decide a relationship would be better governed by fiat, one firm may acquire another—as BHP, a $150bn mining giant, proposed to do with a $35bn rival, Anglo American, on April 24th. Yet between the poles of contract and total commitment are plenty of ways for firms to combine capital, knowledge or other resources, without fully tying the knot.