Some people long for the good old days when we had two big parties − Likud and Labor − competing for the voters’ support, followed by a bunch of small parties, some that would join the coalition formed by the big party that won the election. Some among us maybe even long for the days when there was only one large party − Labor − that formed the coalition.

That’s the way it was for the first 25 years of Israel’s existence when the Labor Party ruled the land, until the election after the Yom Kippur War, in December 1973. Then the two-large-party era began − Likud and Labor competing for control, with at least one of them attaining 40 seats.

Forty seats, a third of the Knesset, can be considered a sufficiently robust anchor around which to form a stable coalition while giving the leading party the strength to govern toward its objectives. Less than 40 for any party raises the specter of coalition instability and difficulties in governing.

It was in the 1996 election that the decline of both Likud and Labor became apparent. Both dropped below 40 seats. And that’s the way it has been to this day. For the time being, at least, the days of two large parties ruling the Israeli political scene seem to be over. Instability is knocking at the door. What happened?

First, the 1996 election was held under the new law calling for direct election of the prime minister, a law that was advertised to provide greater stability and better governance. As should have been expected, it did just the opposite. It provided an opportunity for many voters to split their vote, thus benefiting the smaller parties at the expense of the bigger ones.

In that election Labor received 34 seats and Likud 32. In the next election held under this law, in 1999, it got worse − Labor received 26 seats and Likud 19. The 40-seat mark for a larger party has not been reached since, even though the law for directly electing the prime minister has been abolished. But it has left its mark.

There is another reason for the growing weakness of the two former large parties, Likud and Labor. It is a unique Israeli phenomenon: the crossing of party lines by politicians who have held leadership positions in these parties. These leaders, sometimes leaving their parties after losing an internal election, feel they are bigger than the party they led, that the party has outlived its usefulness. In other words, it’s a signal they think the party is on the way down. It’s a signal that is not lost on many voters.

After occasional defections by leaders of Likud and Labor over the years, a real implosion of the two-party era was set off in 2005 when Ariel Sharon, at the time Likud’s elected leader, left and set up his own party, Kadima, taking with him Ehud Olmert, Shaul Mofaz, Tzipi Livni and Tzachi Hanegbi from Likud, and Shimon Peres, Haim Ramon and Dalia Itzik from Labor. In the following election Kadima received 29 seats, Labor 19 and Likud 12. Things have only gotten worse since. Now two former leaders of Labor, Amir Peretz and Amram Mitzna, have left that party to join Livni, who has left her party.

These desertions only contribute to the instability of the Israeli political system. None of the proposed changes in governance will end them alone. What is needed is a good dose of leadership plus party loyalty by party leaders, whether they win or lose internal elections.