Those are modern questions about modern geographic borders.
And they are historic questions as new as they are old.
Paul told the Romans that all who are led by the Spirit of God are God's children. All?
How do we know? Paul told the Romans that the Spirit tells us so. We are children of God and so are they.
Somewhat disconcerting is the reminder that being in the family does not mean only a showering of familial benefits. Paul adds that since we are sibling of Christ, we will suffer with them. OTOH, since we are siblings, we'll also be glorified with him.
He told the Romans. The Spirit is still doing the reminding. We can receive the witness of the Spirit, even us, even today, and them, too.
Repeat from last year:
Paul reminds us that we are children of God. God's Spirit is within us. The idea did not originate with Paul. Israel spoke of God's Spirit dwelling within their community (Exodus 25:8). Paul recognizes that the Spirit lives within Gentiles as well.
Trinity Sunday is a good time to look at the people around you and consider what it means for you that God's Spirit is within each of them. And it's a good time to consider what it means for your congregation that God's Spirit is dwelling within your church body. What kind of witness are you viewing? What kind of witness are you showing?
(again, I'm thankful to Allen & Williamson's Preaching the Letters.)