If it for some reason wasn't obvious enough for some, here's a helpful side by side.

Lastly. Engels, in 'Relations between the Irish Sections and the British Federal Council' (1872).

Where Engels suggests 'sinking national differences' is 'not internationalism,' but 'attempting to justify and to perpetuate the dominion of the conqueror under the cloak of internationalism'.

Marx to Meyer (1870). Marx re-iterates 'the first condition of' English 'emancipation' is the 'national emancipation of Ireland'.

Marx to Kugelmann (1869), on the Irish Question. Marx expresses the English working-class must first 'take the initiative' in the 'common cause' of Ireland's independence.

Marx to Lafargue's (1870). Marx expresses aiming for British Capitalism's 'weakest link' via Irish revolution.

Marx to Engels, on the Irish Question (1867 - 1869). Marx expresses that for revolution to be possible in England, 'the lever' of revolution must first come in Ireland. Two decades after 'The Communist Manifesto' was published.