The 7 Years War took place between the dates of 1750-1760, and was a war between France and Britain. There were several skirmishes prior to the war, but it was only declared in 1756.
When the war was declared, Britain made heavy military preparations, such as allying with other countries. Despite this, the British wished to avoid a massive war, and this wish was crushed when the French managed to capture an island the British had conquered almost immediately after the war was declared.
The country of Prussia, previously sided with the French, now sided with Britain, decided to attack the country of Saxony. Austria, ally to Saxony and France, rushed to aid it, but was eventually crushed by the might of the Prussian army. Afterwards, Saxony’s army was forced into joining with the Prussian army.
This move shocked most of Europe, and helped the anti-Prussian alliance grow stronger. Also due to Britain being allied with Prussia, they started sending soldiers and money to support them.
The battle for central Europe eventually escalated, lasting as a long heated battle for 6 years. Despite it’s one year of victories after victories, Prussia eventually started falling in power after suffering defeat after defeat in-between the years 1758-1760. However, the support from Britain, support from neighboring ally Hanover, and the determination of their king kept Prussia willing to fight.
However, Prussia’s situation only kept getting worse, after their defeat in the Battle of Kunersdorf, which the king of Prussia, King Frederik III, lost half of his army. The Russians and Austrians, who defeated him, saw an opportunity to destroy Prussia at Berlin, and attempted to advance towards it. However, both armies had to withdraw due to supplies getting low.
Despite their limits being pushed almost several times during the war, Hanover and Prussia did survive it. The death of the Russian Empress saved Prussia from being destroyed by the Russians again.
Russia went to arrange a treaty (The Treaty of St. Petersburg), which meant leaving Austria to fight Prussia alone, giving renewed hope to Frederik. Eventually, Britain grew tired of the war, forcing Frederik to arrange a treaty. This gave birth to the Treaty of Paris.
The French did have some trouble against Hanover, and suffered many losses from them. The British had little to no victories during year 1758, but the tides eventually turned, suddenly bringing success to them during 1759.