reducer1.js

import {combineReducers} from redux;

const someSubFooInitialState = {
  someSubFoo: 1,
  someSubFoo2: 2
}

const someSubBarInitialState = {
  someSubBar: 1,
  someSubBar2: 2
}

const someSubFoo = (state = someSubFooInitialState, action) => {
  /* your reducer logic */
}

const someSubBar = (state = someSubFooInitialState, action) => {
  /* your reducer logic */
}

export default combineReducers({
  someSubFoo,
  someSubBar
});

reducer2.js

import {combineReducers} from redux;

const someSubBazInitialState = {
  someSubBaz: 1,
  someSubBaz2: 2
}

const someSubFoozInitialState = {
  someSubFooz: 1,
  someSubFooz2: 2
}

const someSubBaz = (state = someSubBazInitialState, action) => {
  /* your reducer logic */
}

const someSubFooz = (state = someSubFoozInitialState, action) => {
  /* your reducer logic */
}

export default combineReducers({
  someSubBaz,
  someSubFooz
});

rootReducer.js

import {combineReducers} from redux;

import reducer1 from './reducer1';
import reducer2 from './reducer2';

export default combineReducers({
  reducer1,
  reducer2
});