The decavalcante was always the second league mafia family but why during the prohibition the various italian gabgs didnt merge but decide to join NY families ?

A strong NJ born family should take Atlantic city and the docks and other cities.
Its just my curiosity.

Maybe they wanted independence
Which they they don't really have since they are under the gambinos for 30 + years

This is now,what I mean why in the prohibition wasnt createn a strong family.

Newark did have it own family. It was disbanded by the commission through Joe Profaci, and the family was split between the 5 NYC families, Philadelphia family, and the Decavalcante family. It was powerful, but there were frictions from the old Maranzano and Masseria fued, even though Monaco was killed at the same time as Maranzano to avoid anymore fighting, there were still hostilities within the crews.

Your question about Atlantic City. It was opened as long as one followed by Nucky Johnson's rules. Back then there were two ways to get to the city, by train and by boat. Some mobsters(Philadelphia, Genovese, Gambino, and Newark) showed up there. But most were Jewish mobsters, and Lansky had a person down there that was controlling a lot of the city's gambling through a relative of Frank Erickson, while the strongest Jewish power in Atlantic City was held by Max Hoff of Philadelphia and Joseph Reinfeld of Newark. It was really all about geography, plus many of the Italian mobsters back then were set in the old world mind set, while there were some that were smart, like Luciano and Lucchese. You see a lot more organized crime committed in Northern Jersey than in Southern Jersey, because there were a lot more road up there that were heavily travelled.

From Raab's "Five Families":

"(Anthony) Accetturo's unexpected contribution was historical data about the Mafia's origins in New Jersey that he had absorbed from conversations with mafiosi old-timers. At the creation of the American Mafia organization in 1931, Lucky Luciano had permitted the formation of only one independent New Jersey borgata, a small clan in Elizabeth that became known as the DeCavalcante family. Leaders of more powerful crews in the Newark area were offered a one-time opportunity to join one of the five newly defined New York families. Believing they would have little chance of upward mobility in the largest New York family, which Luciano controlled, most Newark capos aligned themselves with the four other borgatas. Their decisions in 1931 established the strong and lasting presence of all the five major families in New Jersey."

It does not fit with what was happening in the 1930's and 40's in Newark and it's surrounding areas.

Because New Jersey is basically a large suburb of the NYC and Philadelphia metro areas. It's economy is largely dependent on these two areas. Many residents in New Jersey commute to the two cities for work. As Ben Franklin said: "New Jersey “a barrel tapped at both ends."

then why did gotti have to use the decav family to kill weiss on staten island when he had 20 crew like 400 guys capable to hit him. the decavs worked with all the familys i dont understand why we think they werent respected whats the difference between a killer from long island or toms river or whatever that town in nj is. new england vote in the 5 nyc families was the genvese philly was gambino and i think the decavs got fucked cause all 5 familys operate in there area.

Gotti did not have to use the Decav's
He asked them to do him a favor and they were eager to please.

They never had the power and respect as the NYC five families.

Maybe it was worse because they were so close in proximity to the 5 that made it kind of like a slap in the face to them.

At one point the commission told them they could not make any more guys from NY, because if someone got passed over by one of the five, they would cross the river and easily get made into the Decav family.

With all that said they did have a seat on the commission back in the day