The main change over that period has been in the cars, and in the professionalisation and commercialisation of the sport. Manufacturers had entered works cars in rallies, and in their forerunner and cousin events, from the very beginning: the 1894 Paris-Rouen was mainly a competition between them, while the Thousand Mile Trial of 1900 had more trade than private entries.
The First World War brought a lull to rallying. The Monte Carlo Rally was not resuscitated until 1924, but since then, apart from World War II and its aftermath, it has been an annual event and remains a regular round of the World Rally Championship. In the 1930s, helped by the tough winters, it became the premier European rally, attracting 300 or more participants.
Most of the works drivers of the 1950s were amateurs, paid little or nothing, reimbursed their expenses and given bonuses for winning (although there were certainly exceptions, such as the Grand Prix drivers who were brought in for some events). Then in 1960 came arguably the first rallying superstar (and one of the first to be paid to rally full-time), Sweden's Erik Carlsson, driving for Saab.