The Second World War started in 1939, a few years before what was stated above.
But the reason for the poppies, and for November 11th is twofold, but both date back to the First World War (1914-1918)
In Flanders, where some of the fiercest fighting took place, the soldiers (I was going to say "British" soldiers, but there were many from other nations fighting along side the British) fell and died among the poppy fields. The poppies became the flowers at their graves.
In 1918, when Germany was defeated, an armistice was signed at 11am on 11th November.
A few months later a letter was published in a UK newspaper suggesting that it would be a good idea to remember those who had given their lives that we might remain free. The king read the article, and felt this was an appropriate suggestion, and so, ever since, we in the UK have remembered those who have died fighting for our country in various wars.
Remembrance Sunday is the day that we hold the services of remembrance, including the laying of wreaths of poppies at cenotaphs and war memorials around the country.
…As an aside, it also holds significance to those in Northern Ireland, because at one of these services in the 1980s, republican terrorists decided to plant a bomb to murder those at the remembrance service. The person who authorised this act is now the Minister for Education in Northern Ireland…
During the Remembrance services, a verse of a poem by Lawrence Binyon is normally read out. The poem is entitled “For The Fallen”. The day is not a day of nationalistic flag waving or pride, but a day for remembering those who gave their lives, and those who survived to protect our freedom.
For the Fallen
With proud thanksgiving, a mother for her children,
England mourns for her dead across the sea.
Flesh of her flesh they were, spirit of her spirit,
Fallen in the cause of the free.
Solemn the drums thrill: Death August and royal
Sings sorrow up into immortal spheres.
There is music in the midst of desolation
And a glory that shines upon our tears.
They went with songs to the battle, they were young,
Straight of limb, true of eye, steady and aglow.
They were staunch to the end against odds uncounted:
They fell with their faces to the foe.
They shall grow not old, as we that are left grow old:
Age shall not weary them, nor the years condemn.
At the going down of the sun and in the morning
We will remember them.
They mingle not with their laughing comrades again;
They sit no more at familiar tables of home;
They have no lot in our labour of the day-time;
They sleep beyond England's foam.
But where our desires are and our hopes profound,
Felt as well-spring that is hidden from sight,
To the innermost heart of their own land they are known
As the stars are known to the Night;
As the starts that shall be bright when we are dust,
Moving in marches upon the heavenly plain;
As the stars that are starry in the time of our darkness,
To the end, to the end they remain.