The, known as the definite article, is to be used with discrimination. The Oxford English Dictionary gives it 23 definitions, with dozens of sub-entries. The Economist’s use carries some particularities.
We refer to Barclays as a British bank, not the British bank, because there are other British banks, and one of the uses of the is to define. You should not, on first mention, refer to the son of the king if the king has more than one son.
But the is also used for things already mentioned, or so well known that it can be assumed the reader knows them. So Ford, a car company might seem otherworldly when most people expect Ford, the car company. In cases like this, you can, on first mention, add a descriptor: Ford, America’s second-biggest car company. Or if your subject is indeed likely to be known to readers, skip the identifier on first mention, and use a synonym on second mention. Ford announced that it would open a new plant in Spain. America’s second-biggest car company wants to expand its electric-car business in Europe...
Occasionally, the definite article may be optional: Maximilien Robespierre, the leader of the Committee of Public Safety, is preferable to Maximilien Robespierre, leader of the Committee of Public Safety, but in this context the the after Robespierre is not essential. However, Leaders of both mainstream parties means something different from The leaders of both mainstream parties.