The Normans in England belonged to the Capetian dynasty spoke Norman French; this became non-prestigious in France as the variety spoken by the Angevian dynasty in France, Parisian French, became the prestige variety; because Norman French was seen as socially inferior, it was less difficult to abandon it in favour of English;
Subsequently, England became at war with France in the Hundred Years War (1337-1453).
Even as English was on its way in, the gaps in English vocabulary had to be filled by loanwords from French. These include items pertaining to new experiences and ways of doing things introduced by the Normans.
Domains that became enriched with French loanwords include: Government: parliament, government; Finance: treasure, poverty; Law: jury, verdict; War: battle, castle; Religion: charity, saint; Art, fashion, etc.: beauty, colour; Cuisine: bacon, mutton; Household Relationships: uncle, aunt.