What is the order of initialization for static variables?

Question

I'm expecting the following code to output 'AAA ClassA ClassB', but it's only outputing 'ClassA ClassB'. Is my expectation correct? If not, how can I make sure it's initializing all the static variables.

//main.cpp
#include "AAA.h"
#include "ClassB.h"
#include "ClassA.h"

int main()
{
    ClassA::Print();
}

// AAA.h
#pragma once
class AAA
{
public:
    static size_t sSize;
};

// AAA.cpp
#include "AAA.h"
#include "ClassA.h"

size_t AAA::sSize = ClassA::Insert( "AAA" );

// ClassA.h
#pragma once
#include <vector>
#include <string>

class ClassA
{
public:
    static size_t Insert( const std::string& str );
    static void Print();
    static std::vector<std::string> sVec;
    static size_t sSize;
};

// ClassA.cpp
#include "ClassA.h"
#include <iostream>

std::vector<std::string> ClassA::sVec;

size_t ClassA::sSize = ClassA::Insert( "ClassA" );
size_t ClassA::Insert( const std::string& str )
{
    sVec.push_back( str );
    return sVec.size();
}

void ClassA::Print()
{
    for( const auto& str : sVec )
        std::cout << str << std::endl;
}

// ClassB.h
#pragma once
class ClassB
{
public:
    static size_t sSize;
};

// ClassB.cpp
#include "ClassB.h"
#include "ClassA.h"

size_t ClassB::sSize = ClassA::Insert( "ClassB" );

When I debugged in VS, sVec did contain "AAA", but then it gets initialized again to be an empty vector. Then "ClassA" and "ClassB" gets inserted.