Advance sounds good to me - I have to think again on my other answer -Taunt - which would now be
V?U?T Boast in a letter to a relation.
I had considered Act on it but it says a 7-letter word.
My final 2 are interdependent: Increase the strain 9 letters ????A?A?? The final letter would be E if advance is right. Could it be aggravate?
This man invaded England 3 letters N??. Final letter would be G if aggravate were right.