The Netherlands was invaded on the 10th of May 1940, by the 15th of May most of the country had given up, even though some Dutch troops put up some really fierce resistance. Especially the parachute troops the Germans threw in the fight suffered hard. The Germans bombed Rotterdam, one of Europe’s most important harbors. The city center was gone. If you visit Rotterdam today you will see that it has much more open space than other cities in the Benelux. There’s a movie about this event, see link below. . More than 80,000 people lost their home, see German bombing of Rotterdam – Wikipedia This had a huge psychological effect. The Dutch surrendered the next day.
There were several camps in the Netherlands such as Vught, Amersfoort, Westerbork… See Category:Nazi concentration camps in the Netherlands – Wikipedia
Whereas Belgium and France were liberated almost entirely by the late summer of 1944, the Netherlands remained under German occupation. They had to suffer through a particularly harsh winter Dutch famine of 1944–45 – Wikipedia
The book ‘Oorlogswinter’ and the movie based on the book give an idea of how the Netherlands suffered during that winter, but I suspect the reality was much worse. It’s a children’s book, but a good one.
On the 5th of September 1944 The Dutch actually thought they had also been liberated. Spontaneous festivities errupted all over the country. This is called ‘dolle dinsdag’ or ‘mad Tuesday’, the next day they realized that the Germans weren’t going anywhere. See this wikipedia article, the title is in Dutch, but the article is written in English. Dolle Dinsdag – Wikipedia
One of the last German victories of WWII was scored on Dutch soil, the battle of Arnhem, as part of Operation Market Garden, a strategic move by the allies that went horribly wrong and boosted German morale. The allies made plenty of mistakes and even dropped their ammunition in areas held by Germans troops. The German commander Model even quipped: ‘I’ve never fought such a cheap battle.’
We also need to take into consideration that lots of Dutch civilians suffered a great deal in Dutch colonies that were occupied by the Japanese. They were put in camps. In Dutch they are usally called ‘jappenkampen’, ‘jap camps’, see Jappenkampen in Nederlands-Indië – Wikipedia (the article doesn’t exist in English, but you can find more on google). This is an important theme in lots of Dutch novels.
An other good indication that the country suffered quite a bit, is that the guy who was responsible for this region was condemned to death at the Nuremberg trials. See Arthur Seyss-Inquart – Wikipedia who was the Reichskommisar in the Netherlands.
Jews were rounded up rather effectively, the best known example is of course Anne Frank.
The Netherlands did not suffer nearly as much as Poland or the Soviet Union, for example, but it certainly didn’t escape unscathed and it influenced the country very deeply…
It’s also commonly assumed that the Germans stole all the bikes in the Netherlands. And if there’s one thing you shouldn’t touch, it’s a Dutch person’s bike… They are still pissed about that.