Actually, WHY we break on 2 is very easy to trace.

When Pierre returned from his " trip " he evaluated what was being danced in Danzon and Bolero."We " were dancing, at that time period ,the square form of Rumba ( a very close resemblance to Danzon )... so.. it doesnt take much to extrapolate, opening the " box " to a Prep on "1" and break fwd on "2" .

Danzon using a " slow "..1 2; the decision, made by all evidence that ,he changed the Bolero ( on 3 ) to 2. The majority of basic foundation Intern. style Rumba, is essentially, a re-arranged of, if you will,of many of the standarised variations being danced in Bolero at that time ( as you probably already know ).

And, there are some Boleros written in a Son rhythm, and i wonder, if that , also had impact on the decision .

The pieces of the jigsaw are all there, just takes time, to put them in the correct sequence .

As to Clave, yes, its not as dominant in many " pop " type songs that, have been used for the Intern style Rumba, and you know what they say " No Clave.. not Latin " .Its the heart and soul of the genre . Just sayin....

In the old time, the Rumba is counted "Quick Quick Slow" or "2-3-4"?
"No Clave Not Latin" is applied mainly for Latin Music or Latin Dance?
I find to read something about Clave but it only topics around Clave with music, no topic talking about Clave and Latin dance. Any help for suggestion?

I would never count the Rumba in slows and quicks. To those of us who are familiar with a Foxtrot know that a Slow has two beats. By calling the 4 1 as a Slow we stand a very good chance of arriving too early and have nothing to do on beat one having already moved the hip across. It is far better to call beat four as Stop and then beat one as Hip. 2 3 4 1.

I think you may be a little confused ; " Clave " is the instrument that sets the stage, so to speak, for how the music is played. It comes in 2 separate orders. Rumba and Guaracha, 3/2 format ( 5 strikes )
and the Son and Guaguanco are 2/3 .

So.. it depends upon WHOM writes the music, for the style in which they want it played . Some bands do have a habit of "switching " the clave during the song. In essence, a good dancer, will adjust HOW they continue to dance, accordingly ( its important, but really wont affect your dance, if you continued dancing in the same fashion ) .

N.B. The above mentioned Rumba, is NOT the format which you would be dancing as a social dance, in either Intern. or Amer. style.
This is a native form of musical composition, which is danced "Free " form .

It is the root of all latin music ,as it employs only a Clave ,and Tumbao ( a drum ) as an accompaniament .

So..... the dances we dance today, are loosely based upon those formats. The only truer forms left that, are danced socially, appear in some forms of Salsa ( Son for e.g. ).

Latin rhythms, are polyrhythmic , and complex. My suggestion is , for now, consolidate your foundation ,to simple counting methods which work for you . Studying at a deeper level will eventually give you a more complete undarstanding of how( and why ) the dances are constructed, the way they are, tho, in my opinion, the Intern. style has lost its way !

If you want to read more about the genre, there are some excellent articles ( written by musicians and others ) on Salsa Forums .

Hope this helps..

Thank terence2 very much for your explanation. Anyway the relation between Clave and Int. Rumba is still very dim to me

You are not alone !