Sorry, for including so many sentences in a single post. I realized it only later. I included the ones I was doubtful of.
1) Customs duties in imports and exports of raw materials were removed. He was accused of corruption but he survived a change of monarch, when George I died and was succeeded by his brother George II.
2) Walpole’s opponent was the Whig William Pitt, who became Prime Minister in 1766. He started a mercantilist policy, to make England a strong and economically competitive country. His policy led to the establishment of a new set of values based on power, wealth and prestige.
3) In this period England expanded its possessions in India, North America and the Caribbeans. The wealthy merchants controlled the mines and trades.
4) They gained prestige and enabled their children to marry into the aristocracy. The artisans and the craftsmen filled the gap between the upper class and the the poor.
5) They worked long hours for a very low wage. Below them there were the poor who had no political rights, lived in terrible conditions and were affected by serious diseases such as smallpox, scurvy or typhus.
6) Workhouses were places built by the parishes where the poor were maintained at public expense and hired out to factory owners. Coffee-houses were meeting places for important companies, centres of the circulation of news and gathering points were people exchanged opinions.
1. ... corruption, ...
I don't understand this: "he survived a change of monarch" -- let me know what you mean here, and I'll help you word it differently.
2. ... Whig, ... wealth, ...
3. two commas needed
4. OK
5. two commas needed
6. No hyphen needed; one comma needed.