Let’s have a look at the…
Deus, qui beatum Ioannem Baptistam suscitasti,
ut perfectam plebem Christo Domino praepararet,
da populis tuis spiritalium gratiam gaudiorum,
et omnium fidelium mentes dirige
in viam salutis et pacis.
I like the sound of the ends of the clauses – suscitasti… praepararet… gaudiorum and then a big change with salutis et pacis. Remember! These prayers are to be sung! Suscitasti is, as you now recognize, a syncopated form, short for suscitavisti, which would have diminished the rhythmic coherence in the first three clauses.
O God, who raised up blessed John the Baptist,
so that he would prepare a perfect people for Christ the Lord,
grant to your peoples the grace of spiritual joys
and guide the minds of all the faithful into the way of salvation and peace.
CURRENT ICEL (2011):
O God, who raised up Saint John the Baptist
to make ready a nation fit for Christ the Lord,
give your people, we pray,
the grace of spiritual joys
and direct the hearts of all the faithful
into the way of salvation and peace.
This modern Collect of the 1970 Roman Missal is based on the Collect of olden days:
Deus, qui praesentem diem honorabilem nobis in beati Ioannis nativitate fecisti: da populis tuis spiritualium gratiam gaudiorum; et omnium fidelium mentes dirige in viam salutis aeternae.
Perhaps the terrible wars of the 20th century drove the composers of the newer version to include the petition for peace.