We tend to think that bikes always ruled the Netherlands, but in fact after WWII the Dutch pretty much followed the path of other countries and embraced the automobile, destroying entire neighborhoods to make room for the car. Bicycle use dropped from 80 percent to 20 percent and people thought that bikes might disappear altogether.
That all changed in the seventies. Renate van der Zee describes in the Guardian How Amsterdam became the bicycle capital of the world;
All that growing traffic took its toll. The number of traffic casualties rose to a peak of 3,300 deaths in 1971. More than 400 children were killed in traffic accidents that year. This staggering loss led to protests by different action groups, the most memorable of which was Stop de Kindermoord (“stop the child murder”).
Zach Shahan told the same story earlier in TreeHugger, in his post How did bicycling take over the Netherlands? He noted that after the oil crisis of 1973 the governments got on board to push bikes as an alternative to the car. "The 1970s became a period when the Netherlands shifted to a more balanced transportation approach that gave room, infrastructure, and funding to bicyclists and pedestrians." Or as noted in the Guardian,
Gradually, Dutch politicians became aware of the many advantages of cycling, and their transport policies shifted – maybe the car wasn’t the mode of transport of the future after all. In the 1980s, Dutch towns and cities began introducing measures to make their streets more cycle-friendly.
In the Guardian, we learn that it is still a struggle.
“The battle goes on,” says [cyclist union activist] Godefrooij. “The propensity of urban planners to give priority to cars is still persistent. It’s easy to understand: an extra tunnel for cyclists means you have to spend extra money on the project. We’ve come a long way, but we can never lower our guard.”
In North American cities, the battles are really just beginning as cycling is still mired in the single digits in most places and the car still rules. But as seen in the Netherlands and Denmark, activism has a way of becoming mainstream accepted wisdom over time.