How did the Netherlands expand their land?

Answer 1

I'm not entirely sure what you mean by "enlarge their borders" so I'll give answers to the 3 contexts i am at this point able to interpret it on :D

1. in the sense of our actual growth geological measure: we don't go anywhere further than this, confined by all other countries, unless one counts the North Sea area near rotterdam port towards actual dutch borders (which i don't :D), and also confined by actual international rules that limit about any country in the western world to conquer more, Netherlands will not very likely ever grow bigger again

2. a historical sense of "enlarge their borders" as in: infiltrating, and colonizing oarts of the planet that never belonged to the Netherlands...

well, being close to Great Britain and being tradesman by blood, they tended to provide and be financially supported by the English through their tradesmanship, early by trading Asian native spices, later by trading slaves from Africa to work in the then new America (sad but true)

which roughly (and fairly blunty said) concludes: the Netherlands got the money for progressing into one of the technological and finanancial leaders of the western world by providing the English in world domination, and eventually ended up playing a huge part of colonization of the Americas (which includes, even eludes the slave trafficking of African natives on a massive scale)

3. (a bit far fetched, but one never knows) in a sense of recent politic successes towards right-wing politics and the stronger growing introlerance towards immigrants, one could say we enlarged our borders in a symbolic matter... as to why, it's ahrd to answer, fact is dutch citizen quality of life in terms of safety has had a big dent by disturbing incidents which in the majority of the cases turned out to be the result of actions by quite unadapted immigrants (either by chance or by social isolation), which resulted into a huge decrease of trust in the multicultural society the country has been living in, pitching more and more people towards right-wing ideals

Answer 2

We expand our land via recovering land from the sea and in the early ages swamps. Also to create land, what we did to get Maasvlakte II, we use almost the same technique as the one used for Beach nourishment.

Answer 3

Build dykes.

And pump out the water with Windmills.

That makes a Polder