Caribbean Island accepts mistake, sick of opposition to the activity of partisans (13)

'opposition to the activity of partisans' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'caribbean island accepts mistake sick' is the wordplay.
'caribbean island' becomes 'antigua' (I've seen this before).
'accepts' indicates putting letters inside.
'mistake' becomes 'err' (to err is to make a mistake or blunder).
'sick' becomes 'ill' (similar in meaning).
'err'+'ill'='errill'
'antigua' going around 'errill' is 'ANTIGUERRILLA'.

'of' is the link.

Can you help me to learn more?