East has a choice whether to bid 2♣ or 1♦ . 

1♦ followed by a jump rebid to show 6+♦ s and 16+ HCPs is shown.

2♣ to open has 3 losers, so a game in ♦ s without some values or a winner or 2 from partner is not likely.

Over 1♦ a positive response would mean that 5♦ is a good possibility. If partner bids 1♥ there may be a possible slam in ♥ s.

Difficult to find a slam if south supports ♣ s by bidding 5♣ s. If south passed west with no first round controls just bids game with 5♦ s.

Some Souths may bid a pre-emptive 3♣ (due to 2♣ being the strong bid, 3♣ is often bid with only 6♣ s, especially in positions 1 and 3 which are the best positions to pre-empt).

South opens 1NT

North has 19HCPs so a total of 31-33.

Norths 4NT bid is quantitative and asks south to bid 6NT if maximum or has a source of tricks e.g. a 5 card suit.

With neither south passes.

In this case 6NT makes, but it relies on a  finese and K♦ beign on the right side of the ace, so not a good slam to bid.

As you can see many different bidding choices here. Anyone making a positive score stopped bidding so the opposition could go off.

1♣ , not one to pre-empt as your side may have a ♠ fit.

Easy overcall for north with 1♥ .

East has values so could either bid 2♦ not the greatest suit, so some may pass.

South should probably not bid 2NT as north might have a weak overcall, so a double showing 4♠ s is probably best.

West passes and north has a difficult decision, probably can only bid 2♥ s which will be probably passed out.

1NT by east and west transfers to ♠ s by bidding 2♥ s.

A number of possibilities on the bidding.

Some souths could pre-empt in position 1 with 3♣ s. North may then try 3♥ s.

West in position 2 could open a weak 2♦ s if south has passed. North would then bid 2♥ s

Over 2 passes north should probably bid 1NT, showing 12-14 HCPs and balanced hand 5332. 1♥ opening with 5332 often creates a rebid proble.

Over norths 1NT some easts may overcall 2♠ s a borderline decision as shape is more for defence with 5332.

West is not strong enough to bid 3♠ s over the 1♠  response.

East has good intermediates with 10, 9♠ and ♣ s so could invite game by bidding 3♠ s.

West has additional values that have not been shown and the 5♦ s could be useful so bids game.

East has a clear 3♦ pre-empt.

South has not got a good vulnerable 3♥ overcall, so should probably pass.

West can see there is no fit in ♦ s. If west bids a new suit over a pre-empt this is normally played as forcing to game, so east will then raise to game which will go off.

What have you agreed with your partner.

If you have agreed a new suit is not forcing, due to the strange distributions partner may bid again anyway.

Pre-empts cause problems for opposition and sometimes for yourselves, but you do know roughly what your partner has when he pre-empts.

Interesting article on pre-emptive bids. http://www.bridgeguys.com/Conventions/PreemptBids.html

West has a poor 2♦ overcall, but at non-vulnerable will be done often.

North could show support for partner.

East shows ♠ s 

South has an easy 3♥ s following partners support which is passed out.

Some Easts at this vulnerability may bid 3♠ s which will cause many souths to bid 4♥ s.

Only 2♥ or 2♠ s should make, though often you can make an extra trip due to misdefence.