Quoting from the Leiden University website:
The National Archives in Kew, UK hold a treasure that causes real excitement among scholars: the recently rediscovered collection of Dutch documents from the second half of the 17th to the early 19th centuries, comprising over 38,000, both commercial and private, letters. These so-called sailing letters were confiscated during the wars fought between The Netherlands and England.
The research programme Letters as loot: Towards a non-standard view on the history of Dutch aims at exploring this extraordinary and highly valuable source for a new history of Dutch.
The project comprises three sub-projects. Two cross-sections are made in the source material at a chronological distance of about hundred years: the first of the period 1665-1674 (2nd and 3rd Anglo-Dutch Wars) and the second of the period 1776-1784 (4th Anglo-Dutch War and American War of Independence).
Every month, a new letter is translated and posted online. In the Monthly Letter posted in May/June 2009 was a fascinating letter written in 1664 by my ancestor Hendrick Meesen Vrooman to his brother Jacob. Hendrick had recently arrived in New Netherland (present day New York) and wrote to tell his brother Jacob in Leiden all about the new land he had settled in.
What an insight into both my ancestor and the time period when the English took New Netherland and it became New York.
Hendrick says in his letter "Furthermore I let you know that there have arrived three English ships at the Manhattans with soldiers and they have claimed the land and they say that it belongs to their king. And Stuyvesant [the governor of the New-Netherlands] has given it to them without one shot, with an agreement."
I spent an enjoyable hour browsing the other letters held at University of Leiden website. Just choose English from the main page if you do not read Dutch.