What was the failure of the schlieffen plan and why was there a stalemate?

The German Schlieffen Plan was designed to knock France out of the war in 6 weeks,thus allowing 2 weeks for the German army to be moved east to fight the Russians - the vast distances involved,and the underdeveloped state of the Russian transport system meant that it would take the Russian army 2 months to be fully mobilized and ready to attack Germany.

The Schlieffen Plan called for an invasion of neutral Belgium,which would outflank the French army (deployed along the Franco-German border).Once behind Paris,the German army would wheel inwards ,surrounding and capturing the city,and forcing a French surrender.

It failed because Russia launched an immediate attack on East Prussia when the war began,even though its troop weren't fully mobilized yet (this was to lead to disastrous defeats at Tanneberg and the Masurian Lakes within a month).However,when the attack began,Germany was taken bu surprise and,the Kaiser panicked,ordering the immediate withdrawal of 2 army corps from the Schlieffen Plan,to be sent east to combat this threat (the Russians were in fact decisively defeated before these 2 army corps reached East Prussia).

This withdrawal caused a gap in the German front,and general von Kluck,commanding the extreme right wing of the advance,wheeled inwards to close the gap.However,this wheel was made to the east of Paris,not the west,so the city was never surrounded or cut off.Further,the wheel exposed von Kluck's flank,which the French attacked at the First Battle of the Marne,thus halting the German advance.

Both sides now failed to outflank each other to the north,but both failed.As a result,by early 1915 both sides had constructed continuous trench lines that reached from the Belgian North Sea Coast to the Swiss border,and so the war bogged down into trench warfare,which produced a stalemate as neither side could break through.

Ok, this is the third question I have seen on the Schlieffen plan from you, why not read up on it a bit. If you read the first question that I responded to, you will see that I said that it was the only plan in the German playbook in the early 20th century. It was for fighting a two-front war against France and Russia, and based on the idea that Russia would be slow to mobilize. So hit France hard first, then move troops by rail to Eastern front. Problem was that the Russians mobilized faster than expected. Also the new technologies of war changed the way that war was waged, so the Western front just stalled. Read a bit more for yourself, this is just a vague outline.