MP needs support entering global alliance: plenty given! (7)
I believe the answer is:
umpteen
'plenty given' is the definition.
(umpteen means a large number)
'mp needs support entering global alliance' is the wordplay.
'needs' means one lot of letters go next to another.
'support' becomes 'tee' (tee is a kind of support).
'entering' means one lot of letters goes inside another.
'global alliance' becomes 'UN' (United Nations).
'mp'+'tee'='mptee'
'mptee' going inside 'un' is 'UMPTEEN'.
(Other definitions for umpteen that I've seen before include "Indefinitely large number" , "Large but indefinite number" , "Informally, very many" , "An uncountable number" , "Uncountably many" .)