It needs to be more specific
The Germans wanted the British government to ignore the Treaty of London and let the German army pass through Belgium. ... In the end, Britain refused to ignore the events of 4 August 1914, when Germany attacked France through Belgium. Within hours, Britain declared war on Germany.
It caused widespread panic and started a depression.
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Answer:
The most convincing 'internal' factor behind southern defeat was the very institution that prompted secession: slavery. Enslaved people fled to join the Union army, depriving the South of labour and strengthening the North by more than 100,000 soldiers. Even so, slavery was not in itself the cause of defeat.