load all content on 1 page

The basic WordPress setup only calls out the last 10. You'll need to make your own query to be able to run more posts through.

Try this out:

<?php get_header(); ?>          


<article>

    <?php
        $query = new WP_Query( 'posts_per_page=-1' );
        while ($query->have_posts()) : $query->the_post(); 
    ?> 

        <div class="index">
            <div class="thumb"><?php the_post_thumbnail('')?> </div>
        </div>

    <?php endwhile; ?>
</article>

<?php get_sidebar(); ?>

<?php get_footer(); ?>

The full explanation can be found in the codex.

Details about the usage above can be found HERE

the problem is you are running this with Standard WordPress Loop . Normally the standard WordPress Loop is bounded to ten. This you can change in Settings -> Reading -> Blog pages show at most

but if you don't want to change it there you need to put this before the loop

wp_reset_query();
query_posts( 'posts_per_page=10000' ); // will proably show 10000 now as seen in the other answers -1 should show all

which starts with

<?php while (have_posts()) : the_post(); ?> 

http://codex.wordpress.org/Function_Reference/query_posts https://codex.wordpress.org/Function_Reference/wp_reset_query

so far so good?